Section 4

GROUND SURVEYS FOR PRIMARY CONTROL


 

 

 

4-01     GENERAL DESCRIPTION

Ground control consists of a system of points for a given project whose positions are known and referenced to a ground coordinate system, such as the New Jersey State Plane Coordinate System of 1983 (NJSPCS 83) or the North American Datum of 1983 (NAD 83), and whose images can be positively identified in corresponding aerial photographs.  Such control is established by means of field surveys and provides the means for precisely orienting and scaling the photographs to the ground.

4-02     MATERIALS AND EQUIPMENT

All materials and equipment required to satisfactorily complete all control surveying work shall be furnished by the Contractor unless stipulated otherwise by the NJDOT.  Said equipment shall be fully capable of accomplishing the control surveying to the accuracies specified by the NJDOT.

At the request of the NJDOT, the Contractor will submit documentation showing the latest calibration tests that have been performed, together with the results of these tests, on all survey equipment used or intended for use by the Contractor on the Project.  Similarly, all equipment used or intended for use by the Contractor for ground control will be made readily available to the NJDOT for inspection.

4-03     LIAISON

Prior to executing any ground surveys, the Contractor or his authorized representative shall meet with the designated NJDOT representatives, including personnel from the NJDOT Geodetic Survey Unit at the discretion of the NJDOT, for the following purposes:

4-04     GROUND CONTROL

All ground surveying and related analytical work required to execute primary or basic control surveys shall be accomplished by the Contractor in accordance with the procedures and accuracies as specified by the NJDOT.  All control points shall be set from and closed on existing National Geodetic Survey (NGS) monuments;  NJDOT Geodetic Survey (NJGS) triangulation; or GPS, traverse stations which meet second or higher order accuracy surveys and are part of the National Geodetic Survey Data Base.  If the Contractor has utilized any control monuments other than existing NGS or NJGS controls, the Contractor shall certify that the ground control meets the accuracies and standards specified by the NJDOT.  The Contractor shall also provide the NJDOT with certification, signed and sealed by a qualified Land Surveyor (see Section 1-05), that the accuracies and standards specified by the NJDOT have been met.

All primary and other basic control surveys must begin and close on at least two separate existing control points or, if approved by the NJDOT, such surveys shall be closed-circuit in character.

Those control points which are used as origin, intermediate check, and  closure points shall be points comprising closed primary traverses and closed level circuits.  Primary or other basic control surveys shall measure accurately each required control point, and accuracy checks shall be made on the surveying work as a whole.

Control points consisting of monuments or station markers and bench marks which are set by the Contractor shall be numbered consecutively from the beginning of the Project to the end for each traverse and level run.  Each traverse shall be identified with a letter designation starting with the first letter of the alphabet, and each level run shall receive a letter designation starting with the last letter of the alphabet and working backwards.

Semi-permanent monuments, station markers, and other control points shall be set along the traverse routes at the minimum rate of two (2) intervisible pair per kilometer of traverse length. A minimum of four (4) bench marks per kilometer of traverse length shall be set.  These control points shall not be placed in roadway or shoulder pavement unless such placement has been approved by the NJDOT. Control points can also be set by chiseling crosses in concrete structures or rock outcrops.

All monuments or station markers, bench marks and any other control points placed by the Contractor shall be tied and referenced in the field.

4-04.1  Permanent Monuments or Survey Station Markers

  1. Materials:  Permanent monuments or survey station markers in first and second order surveys shall be bronze or brass plugs or aluminum alloy tablets set in iron pipes, in copper-coated steel rods, in concrete monument foundations, or cemented in large solid rocks or boulders. The Contractor shall furnish all plugs or tablets, and other necessary parts of a design as illustrated in Figures 4-1, 4-2, 4-3 and 4-4.

     

    In third-order surveys, semi-permanent monuments and station markers shall be pins of nineteen millimeters (19 MM) or more in diameter and not less than nine tenths of a meter (0.9 M) long, or they shall be as specified in the preceding paragraph.

     

    Within the public domain or subject to a clear, legally binding agreement with the affected property owner(s), set reference marks shall consist of nails or spikes driven into large trees which are nonornamental and do not bear fruit; of lead plugs drilled in walls, abutments, solid rock outcrops and like objects which are permanent in character; or they may consist of steel T-bars.
  2.  

  3. Control:  All permanent monuments and station markers and their references shall be set where they will not be disturbed by normal land use.  Wherever practicable, such markers shall be placed near some easily recognizable feature and in an accessible location.  Such placement shall be preferably established outside future construction sites but within the right-of-way boundaries of the proposed project.  At least three (3) references shall be accurately placed so that the markers may be recovered or reset readily on any subsequent field surveys.  Ties to the references must be accurately measured with a steel tape or EDM so that it will be possible to make an accurate intersection of three predetermined measurements to facilitate recovering each control point.  Such references shall be of the semi-permanent type and shall be so located as to be visible from and accessible to the station marker to which it applies.

     

    Semi-permanent reference marks may consist of spikes driven into trees, well-established fence lines, and durable marks set in rock outcrops, footings, building walls and the like.  Where such suitable features are not available, a steel T-bar, which is no less than nine tenths of a meter (0.9 M) long with a special distinctive cap in which the reference cross has been imprinted, shall be set to serve in its place.

     

    In the field notes, the Contractor shall clearly sketch to scale and otherwise describe the surveyed position of each permanent station marker together with its reference data.  The Contractor shall also record any azimuth marks for those markers which are not intervisible for subsequent plotting on the maps.  The bearing on the New Jersey State Plane Coordinate grid shall be noted between each station marker and its adjacent visible markers.  The New Jersey State Plane Coordinates for each permanent station marker shall also be recorded.

     

    Each existing and new project permanent survey station marker shall be appropriately identified in its correct New Jersey State Plane Coordinate position on the maps and shall be numbered, named and/or stationed in the format stipulated by the NJDOT.  The following data shall accompany the record of each marker on the maps:  the number designation, the New Jersey State Plane  Coordinates and, if a previously existing marker, the contract designation under which it was either set or last reset and surveyed.  Except for the horizontal position and classification number, all identification data for each marker shall be recorded on the maps as marginal inserts.

     

    Each marker position shall be indicated by a symbol in the overlap portion within each aerial photograph of the applicable stereoscopic pair.  Said symbol shall consist of a photographic image showing a circle rendered thereon in the correct New Jersey State Plane Coordinate position.

     

    A description card shall be prepared containing the following information:

     

    (1)      Name, number or station.
  4.  

    (2)      Municipality and County.

     

    (3)      Mile marker and station if on a State Highway.

     

    (4)      Order of accuracy.

     

    (5)      New Jersey State Plane Coordinate System (NJSPCS 83).

     

    (6)      North American Vertical Datum of 1988 (NAVD 88) elevation in meters.

     

    (7)      Name of Contractor or agency making the control survey.

     

    (8)      Date the monument or station marker was set.

     

    (9)      Complete description of location and type of marker.  This description should include information on how to reach the general location of the Station Site from a town or from some prominent feature normally displayed on maps, and distance from a major roadway intersection.

     

    (10)     Sketch showing distance, true bearing and New Jersey State Plane Coordinate grid bearing to each adjacent station marker, control point and reference point.

     

    These descriptions shall become a part of the Survey Control Report as described in Section 4-08.2.

4-04.2  Survey Bench Marks

  1. Materials:  Survey bench marks shall be bronze or brass plugs or aluminum alloy tablets either set in iron pipes, copper-coated steel rods, or concrete monument foundations, or cemented in large solid rocks or boulders as illustrated in Figures 4-1, 4-2, 4-3 and 4-4.  Iron or other pins less than nineteen millimeters (19 MM) in diameter and less than nine tenths of a meter (0.9 M) long shall not be used.  All plugs or tablets shall be furnished by the Contractor.  The heads of the plugs or tablets shall be approximately seventy-six millimeters (76 MM) in diameter.

     

    When permanent or semi-permanent objects cannot be found to serve as reference for bench mark ties, references shall then consist of lead or copper nails plugging holes drilled in either concrete, large boulders or rock outcrops, or nineteen millimeters (19 MM) or larger diameter metal pins at least nine tenths of a meter (0.9 M) long as field circumstances dictate.
  2.  

  3. Control:  All bench marks shall be set where they will not be disturbed by normal land use.  Wherever practicable, such bench marks shall be placed near some easily recognizable feature and in an accessible location.

     

    Within the public domain or subject to a clear, legally binding agreement with the affected property owner (s), at least two (2) references shall be accurately placed so that the bench marks may be recovered readily on any subsequent field survey.  Such references shall be of the semi-permanent type and shall be so located as to be visible from and accessible to the bench mark to which it applies.  Semi-permanent reference marks may consist of spikes driven into trees which are non-ornamental and do not bear fruit, well established fence lines, and durable marks set in rock outcrops, footings, building walls and the like.  Where such suitable features are not available, a steel T-bar, which is no less than nine tenths of a meter (0.9 M) long with a distinctive cap in which the reference cross has been imprinted, shall be set to serve in its place.

     

    Subject to inspection and approval by the NJDOT Geodetic Survey Unit, all elevations shall be referenced to the North American Vertical Datum of 1988 (NAVD 88) unless specified otherwise by the NJDOT.

     

    Existing bench marks serving as origin or closing ties in the ground control surveys may be appropriated as project bench marks whenever they are in position to serve as such.  In the field notes, the Contractor shall sketch to a reasonable scale the position of each existing bench mark used, and he shall record the identifying number and description of that bench mark.  The Contractor shall not mark, stamp or otherwise deface or disturb any existing bench mark.

     

    Each bench mark utilized for the project within the mapped area shall be identified on the maps by a symbol in the correct New Jersey State Plane  Coordinate position.  Near that symbol, the identifying number and New Jersey Geodetic Survey-based elevation of that bench mark shall be correctly and clearly recorded.  In addition, the position of each bench mark shall be represented by the same symbol in the overlap portion within each aerial photograph of the applicable stereoscopic pair of such photographs. Said symbol shall consist of a photographic image showing a circle rendered in the correct New Jersey State Plane Coordinate position on the photograph.

4-04.3  Semi-permanent Survey Station Markers

  1. Materials:  Semi-permanent station markers shall consist of either: a cross in a lead or copper nail plugging a hole drilled in concrete, a rock outcrop or a large boulder; a cross in the top of a 19 MM x 460 MM T-bar of galvanized steel that has been driven flush with the ground or to a depth of 250 MM below the surface of the ground when in an open field; or a metal pipe 13 MM to 25 MM in diameter, 610 MM to 760 MM long, or a solid metal pin, twenty millimeters (20 MM) or more in diameter, of similar length.
  2.  

  3. Control:  Semi-permanent station markers shall be set at as many instrument setup points in the required surveys as practicable.  Where feasible, they shall also be set at points targeted on the ground before photography for certainty in identification of supplemental control points to be used in photographic control during the photogrammetric compilation process.

     

    In the field notes, the Contractor shall sketch to scale and shall fully identify and otherwise describe all semi-permanent station markers.  These markers shall be survey-tied from primary or basic control survey points to objects that are visible on aerial photographs, or they shall have a suitable photographic target centered over them on the ground before aerial photographs are taken.

     

    Each semi-permanent station marker within the mapped area shall be appropriately identified on the maps and shall be stationed or numbered in the format stipulated by the NJDOT.  Such identification shall be made with respect to the New Jersey State Plane Coordinate System.

4-04.4  Primary Horizontal Control

The Contractor shall establish at least one primary closed traverse and/or triangulation or trilateration network or GPS network as needed throughout and generally parallel to the longer dimension of the Project.  Unless specified otherwise by the NJDOT, the traverse closure shall not exceed the lesser of either one part in twenty thousand (1:20 000) of the total traverse length, or 0.20 meters times the square root of the total traverse length in kilometers after azimuth adjustments, the result being in terms of meters.  Classification, standards of accuracy and general specifications for horizontal controls for traverse, triangulation and trilateration are tabulated in Tables 4-1 and 4-2. All adjustments shall be based on Least Squares Adjustment.

Each and every horizontal control station shall be an integral part of its respective traverse, and all such stations shall be so set upon with angular and distance measuring equipment that each angle and distance is observed directly from station to station and not computed from an alternate point.  Each control station is set in the field with a semi-permanent station marker consisting of a cross marked on a nail plugging a hole drilled in a concrete structure or rock outcrop, footing, building wall and the like.

All station markers shall either be intervisible or require that an azimuth mark be established for each non-intervisible station marker.  The azimuth mark shall be placed anywhere between one hundred to three hundred meters (100 M - 300 M) away from the station marker to insure that the bearing determined by an instrument set over the marker and sighted on the azimuth mark is accurate to within fifteen seconds (+15") of arc.

Cultural features which are permanent, suitable and easily identifiable shall be acceptable as azimuth marks.  If such objects are not available, azimuth marks shall be identified as such from spikes driven into large trees which are non-ornamental and do not bear fruit, metal plugs in drilled holes, and crosses chiseled in concrete structures and rock outcrops, as field circumstances dictate.

All primary horizontal control points and stations shall be field-referenced with at least three (3) well placed ties.

All angles shall be turned with a one-second (1¢¢) direct reading theodolite, and approved methods shall be employed to guarantee the following results:

 

Table 4-1:       Classification, Standards of Accuracy, and General Specifications for Horizontal Control

 

CLASSIFICATION

FIRST-ORDER

SECOND-ORDER

THIRD-ORDER

 

 

CLASS I

CLASS II

CLASS I

CLASS II

TRAVERSE :

Recommended spacing of principal stations

 

Network stations 10-15 KM;  other surveys seldom less than 3 KM

Principal stations seldom less than 4 KM except in metropolitan area surveys where the limitation is 0.3 KM

Principal stations seldom less than 2 KM except in metropolitan area surveys where the limitation is 0.2 KM

Seldom less than 0.1 KM in tertiary surveys in metropolitan area surveys;  required for other surveys

Horizontal directions or angles2

 

Instrument

0.”2

0.”2 } or { 1.”0

0.”2 } or { 1.”0

1.”0

1.”0

 

Number of Observations

16

8     } or { 12

6     } or { 8

4

2

 

Rejection limit from mean

4”

4”    } or { 5”

4”    } or { 5”

5”

5”

Length measurements

 

Standard error1

1 part in

600 000

1 part in

300 000

1 part in

120 000

1 part in

60 000

1 part in

30 000

Reciprocal vertical angle observations3

 

Number of and spread between observations

3 D/R-10”

3 D/R-10”

2 D/R-10”

2 D/R-10”

2 D/R-20”

 

Number of stations between known elevations

4-6

6-8

8-10

10-15

15-20


TABLE 4-1:     Classification, Standards of Accuracy, and General Specifications for Horizontal Control (cont.)

CLASSIFICATION

FIRST-ORDER

SECOND-ORDER

THIRD-ORDER

 

 

CLASS I

CLASS II

CLASS I

CLASS II

TRAVERSE :

Astro azimuths

 

Number of courses between aximuth checks5

5-6

10-12

15-20

20-25

30-40

 

Number of observations per night

16

16

12

8

4

 

Number of nights

2

2

1

1

1

 

Standard error

0.”45

0.”45

1.”5

3.”0

8.”0

 

Azimuth closure at azimuth checkpoint not to exceed6

1.”0 per station or 2”ÖN

1.”5 per station or 3”ÖN

Metropolitan area surveys seldom to exceed 2.”0 per station or 3”ÖN

2.”0 per station or 6”ÖN

Metropolitan area surveys seldom to exceed 4.”0 per station or 8”ÖN

3.”0 per station or 10”ÖN

Metropolitan area surveys seldom to exceed 6.”0 per station or

 15”ÖN

8” per station or

 30”ÖN

Position closure4,6

 

after azimuth adjustment

0.04 M ÖK or   1:100 000

0.08 M ÖK   1:50 000

0.2 M ÖK     1:20 000

0.4 M ÖK    1:10 000

0.8 M ÖK      1:5 000

1.        The standard error is to be estimated by

                                                                                                         ( __åy2__ )1/2

                                                                                                s=M= (   n(n-1)  )1/2

 

where sM is the standard error of the mean, v is a residual (that is, the difference between a measured length and the mean of all measured lengths of a line), and n is the number of measurements.

 

The term “standard error” used here is computed under the assumption that all errors are strictly random in nature.  The true or actual error is a quantity that cannot be obtained exactly.  It is the difference between the true value and the measured value.  By correcting each measurement for every known source of systematic error, however, one may approach the true error.  It is mandatory for any practitioner using these table to reduce to a minimum the effect of all systematic and constant errors so that real accuracy may be obtained.  (See page 267 of Coast and Geodetic Survey Special Publication No. 247, Manual of Geodetic Triangulation, Revised edition, 1959, for definition of “actual error”.)

2.        The figure for “Instrument” describes the theodolite recommended in terms of the smallest reading of the horizontal circle.  A position is one measure, with the telescope both direct and reversed, of the horizontal direction from the initial station to each of the other stations.  See FGCC “Detailed Specifications” for number of observations and rejection limits when using transits.

3.        See FGCC “Detailed Specifications” on “Elevation of Horizontal Control Points” for further details.  These elevations are intended to suffice for computations, adjustments, and broad mapping and control projects, not necessarily for vertical network elevations.

4.        Unless the survey is in the form of a loop closing on itself, the position closures would depend largely on the constraints or established control in the adjustment. The extent of constraints and the actual relationship of the surveys can be obtained through either a review of the computations, or a minimally constrained value adjustment of all work involved.  The proportional accuracy or closure (i.e., 1/100 000) can be obtained by computing the difference between the computed value and the fixed value, and dividing this quantity by the length of the loop connection the two points.

5.        The number of azimuth courses for first-order traverses are between Laplace azimuths. For other survey accuracies, the number of courses may be between Laplace azimuths and/or adjusted azimuths.

6.        The expressions for closing errors in traverses are given in two forms.  The expression containing the square root is designed for longer lines where higher proportional accuracy is required.

                The formula that gives the smallest permissible closure should be used.

                N is the number of stations for carrying azimuth.

                K is the distance in kilometers.

(Federal Geodetic Control Committee. (1975) 1980. Classification, standards of accuracy, and general specifications of geodetic control surveys.  Reprint.)

Table 4-2:       Classification of Triangulations

CLASSIFICATION

FIRST ORDER

SECOND ORDER

THIRD ORDER

 

 

CLASS I

CLASS II

CLASS I

CLASS II

TRIANGULATION :

Recommended spacing of principal stations

 

Network stations seldom less than 15 KM;  metropolitan surveys 3 to 8 KM and others as required

Principal stations seldom less than 10 KM; other surveys 1 to 3 KM or as required

Principal stations seldom less than 5 KM or as required

As required

As required

Strength of figure R1 between bases

 

Desirable limit

20

60

80

100

125

 

Maximum limit

25

80

120

130

175

 

Single figure desirable limit

 

 

 

 

 

 

R1

5

10

15

25

25

 

R2

10

30

70

80

120

 

Single figure maximum limit

 

 

 

 

 

 

R1

10

25

25

40

50

 

R2

15

60

100

120

170

Base measurement

 

Standard errora

1 part in

1 000 000

1 part in

900 000

1 part in

800 000

1 part in

500 000

1 part in

250 000

Horizontal directions

 

Instrument

0.”2

0.”2

0.”2 } or { 1.”0

1.”0

1.”0

 

Number of positions

16

16

8     } or { 12

4

2

 

Rejection limit from mean

4”

4”

5”    } or { 5”

5”

5”

Triangle closure

 

Average not to exceed

1.”0

1.”2

2.”0

3.”0

5.”0

 

Maximum seldom to exceed

3.”0

3.”0

5.”0

5.”0

10.”0

Side checks

 

In side equation test, average correction to direction not to exceed

0.”3

0.”4

0.”6

0.”8

2”

Astro azimuths

 

Spacing figures

6-8

6-10

8-10

10-12

12-15

 

Number of observations per night

16

16

16

8

4

 

Number of nights

2

2

1

1

1

 

Standard error

0.”45

0.”45

0.”6

0.”8

3.”0

Vertical angle observations

 

Number of and spread between observations

3 D/R-10”

3 D/R-10”

2 D/R-10”

2 D/R-10”

2 D/R-20”

 

Number of figures between known elevations

4-6

6-8

8-10

10-15

15-20

Closure in length (also position when applicable)

 

after angle and side conditions have been satisfied should not exceed

1 part in

100 000

1 part in 50 000

1 part in 20 000

1 part in 10 000

1 part in 5 000

(Courtesy National Ocean Survey.  Reprint)

4-04.5  Primary Vertical Control

The Contractor shall establish at least one primary closed level circuit as needed throughout and generally parallel to the longer dimension of the Project.  Each level circuit shall be established by following the accepted procedures of differential leveling.  No trigonometric leveling shall be permitted, and no "spur" or "hanging" vertical points shall be accepted.

All primary or basic vertical control shall be extended from and closed on National Geodetic Survey Bench Marks of second or higher order accuracy and shall be of second order accuracy.  All vertical control positions shall be referenced to the North American Vertical Datum of 1988 (NAVD 88).  The Contractor shall adjust all vertical elevations to the North American Vertical Datum of 1988 (NAVD 88), unless approved otherwise by the NJDOT.  All vertical control circuits required for the Project other than the primary circuit (s) shall begin and close on the level network of primary elevation control set and surveyed by the National Oceanic and Atmospheric Administration (NOAA) unless approved otherwise by the NJDOT.

Semi-permanent bench marks shall be set at the approximate rate of two for each kilometer of bench level route and shall not be set further apart vertically than ten meters (10 M) difference in elevation.  Such bench marks shall be of second order accuracy unless specified otherwise by the NJDOT.

Second order Class II vertical accuracy shall be defined as having a minimum error vertical closure of 8 millimeters (8 MM) times the square root of the length of the level circuit in kilometers [8 MM (K)1/2] (see Table 4-3).  All bench level lines shall be properly adjusted to minimize if not eliminate any error contained therein.

At least two (2) well placed ties shall be required to field-reference each vertical control point established by the Contractor.

Table 4-3:       Classification, Standards of Accuracy, and General Specifications for Vertical Control

CLASSIFICATION

FIRST-ORDER

SECOND-ORDER

THIRD-ORDER

 

CLASS I, CLASS II

CLASS I

CLASS II

 

Principal uses

Basic framework of

Secondary control of

Control densification,

Miscellaneous local

 

Minimum standards;  higher accuracies may be used for special purposes

the National Network and of metropolitan area control

the National Network and of metropolitan area control

usually adjusted to the National Net.  Local engineering projects

control may not be adjusted to the National Network.

 

 

Extensive engineering projects

Large engineering projects

Topographic mapping

Small engineering projects

 

 

Regional crustal movement investigations

Local crustal movement and subsidence investigations

Studies of rapid subsidence

Small-scale topographic mapping

 

 

Determining geopotential values

Support for lower-order control

Support for local surveys

Drainage studies and gradient establishment in mountainous areas

Recommended spacing of lines

Net A; 100-300 KM class I

Secondary net;

20-50 KM

Area control;

10-25 KM

As needed

 

National Network

Net B; 50-100 KM class II

 

 

 

 

Metropolitan control;

2-8 KM

0.5-1 KM

As needed

As needed

 

other purposes

As needed

As needed

As needed

As needed

Spacing of marks along lines

1-3 KM

1-3 KM

Not more than 3 KM

Not more than 3 KM

Gravity requirement

0.20 x 10-3 gpu

 

 

 

Instrument standards

Automatic or tilting levels with parallel-plate micrometers; invar scale rods

Automatic or tilting levels with optical micrometers or three-wire levels; invar scale rods

Geodetic levels and invar scale rods

Geodetic levels and rods

Field procedures

Double-run; forward and backward, each section

Double-run; forward and backward, each section

Double- or single-run

Double- or single-run

 

Section length

1-2 KM

1-2 KM

1-3 KM for double-run

1-3 KM for double-run

 

Maximum length of sight

50 M class I; 60 M class II

60 M

70 M

90 M

Field proceduresa

 

 

 

 

 

Max. difference in lengths

 

 

 

 

 

Forward and backward sights per setup

2 M class 1; 5 M class II

5 M

10 M

10 M

 

per section (cumulative)

4 M class I, 10 m class II

10 M

10 M

10 M

 

Maximum length of line

Net A; 300 KM

 

50 KM double-run

25 KM double-run

 

between connections

Net B; 100 KM

50 KM

25 KM single-run

10 KM single-run

Maximum closuresb

 

 

 

 

 

Section; forward and backward

3 MM ÖK class I,

4 MM ÖK class II

6 MM ÖK

8 MM ÖK

12 MM ÖK

 

Loop or line

4 MM ÖK class I,

5 MM ÖK class II

6 MM ÖK

8 MM ÖK

12 MM ÖK

aThe maximum length of line between connections may be increased to 100 KM for double-run for second-order class II, and to 50 KM for double-run for third-order in those areas where the first-order control has not been fully established.

bCheck between forward and backward runnings, where K is the distance in kilometers.

(Federal Geodetic Control Committee. (1975) 1980. Classification, standards of accuracy, and general specifications of geodetic control surveys.  Reprint.)

4-05     SURVEY TRAVERSE FOR CADASTRAL SURVEYS

This section shall apply when cadastral (property boundary) surveys are required in conjunction with the compilation of large-scale maps.  Cadastral surveys are to be tied in with conventional surveying and GPS surveying methods to the primary control points as represented by station markers.  These markers comprise the primary control traverse to be surveyed and otherwise shall be intervisible and spaced as specified by the NJDOT.

In areas where the width of the survey area is increased, additional traverses shall be surveyed as needed.  Wherever multiple flight strips are essential for accomplishing the required mapping, a traverse shall be surveyed lengthwise along the approximate center of each strip.  All such traverses shall be executed as closed traverses within the primary horizontal control of the Project.

All resulting survey data shall be noted and drawn on the map(s) and shall include each instrument point, each survey origin/closure set of ties to primary control, and the distances and New Jersey State Plane Coordinate bearings of each traverse segment.  Closure ties shall either be shown at their location on the map(s) or they shall be marginal inserts wherever their corresponding principal control points lie outside the mapped area.  Each control point and each instrument point shall be plotted accurately and designated by its New Jersey State Plane Coordinates.

4-06     LOCATING MONUMENTS ON MAPS

The location of each monument, which is set and otherwise utilized by the Contractor, shall be indicated on the maps in conjunction with its corresponding identifying data:  number designation, its New Jersey State Plane Coordinates, the elevation, if any, and information tying the monument to a primary survey line or other appropriate field-established reference(s) to facilitate future recovery.  Except for showing the positions of those monuments actually situated within the areas covered by the maps, all annotations shall be recorded in marginal inserts.

Whenever existing control monuments are taken from previous mapping contracts, whether prepared for the NJDOT or another agency or client, the original contract project designation and its corresponding "as built" date shall be noted on the maps.

4-07     SUPPLEMENTAL CONTROL SURVEYS

Whenever supplemental control is to be established from ground surveys, the Contractor shall execute those surveys so that corresponding aerial photographs can be correctly positioned and oriented onto precision photogrammetric mensuration instruments.  These instruments shall be capable of providing measurements to a precision of one (1) micron, and they shall be calibrated over the measuring range of the Project to an accuracy sufficient to achieve a root mean square error of no more than two (2) microns.  The Contractor shall utilize only fully analytical aerial triangulation methods to establish supplemental photo control. Semi-analytic or analog methods shall not be permitted.

4-07.1  Horizontal Control

A minimum of three (3) horizontal control points is required for each stereoscopic model although a fourth point is recommended as a check, and these points shall be as far apart as is feasible within each model.  Each model point shall be an image of an existing object in the field, or it shall be part of a finite photographic pattern which is readily identifiable on the ground in the photographs, or it shall be the photographic target of a station marker.  The X and Y coordinates of horizontal control shall be subsequently computed for each supplemental control point with respect to the New Jersey State Plane Coordinate System.

4-07.2  Vertical Control

In each stereoscopic model, there shall be at least six (6) vertical control points, one of which shall be near the center of the model and approximately halfway between the principal point of the first aerial photograph and its corresponding image on the adjacent photograph.  The other points shall be spaced for optimum use of the model and preferably so as to include one in or near each corner of the model.  Wherever cross sections are to be measured photogrammetrically, there shall be at least three (3) additional vertical control points spaced appropriately throughout the measuring and mapping area of each model.  The elevation (or Z coordinate) of vertical control, as referenced to the North American Vertical Datum of 1988, shall be ascertained for each supplemental point.

4-07.3  Supplemental Photo Control - Analytical Aerotriangulation

If so elected by the Contractor and upon approval by the NJDOT, analytical aerotriangulation methods may be employed to generate supplemental control points and to compute the required corresponding coordinate data.

In order to carry out analytics, all ground control points must be pre-targeted in accordance with Figure 2-1, with the exception of maximum interval.  When controlling projects designed for analytical aerotriangulation, the maximum interval for horizontal control points shall be no more than five (5) stereomodels, and for vertical control points, no more than two (2) stereomodels.

The beginning and end of all flight lines must be controlled by three (3) horizontal and vertical control points.

The analytical computations must result in a minimum root mean square error at the control points of one part in ten thousand (1:10 000) of the flight height.

A minimum of nine (9) precisely mark supplemental control points will be established for each photograph and six (6) points will be located as near as possible to the corners and the nadir point of the neat model.

The process is initiated with the precise marking of glass photographic diapositives to be used for mapping compilation at those locations where supplemental control is required.  All point-marking shall be done using a precision stereoscopic marking device.  Such marks shall not be smaller than forty (40) microns no larger than one hundred (100) microns, and they shall be appropriate in size to the scale of the photographs and the stereoscopic plotting instruments.  All marks shall be drilled clearly through the emulsion of the diapositives, and excess waste material shall be removed carefully from the surface prior to the mensuration operation.

Each diapositive shall be placed in a mono- or stereo- comparator, having a precision of one (+1) micron, which shall then be used to measure the locations of the supplemental control points and the field-surveyed control points relative to the photo-coordinate system formed from the fiducial marks on that diapositive.  The comparator shall be calibrated over the measuring range to be used on this Project to an accuracy sufficient to achieve a root mean square error of two (2) microns.

The measurements of both sets of control points, the X, Y and Z grid coordinates of the field surveyed control points, and the camera calibration data, shall be entered together into a computer which will then generate the ground coordinates for the supplemental control points.  The computer software utilized shall contain a fully analytical block aerotriangulation program.  This program and the density of the control network shall work in conjunction with each other so that the accuracies required by the NJDOT are met.  As a minimum, this program shall incorporate the capability to give appropriate weight factors to the control points on an individual basis and to correct for film deformation, atmospheric refraction, earth curvature and lens distortion.

4-08     DOCUMENTATION

4-08.1  Field Notes

The field notes of all horizontal and vertical control surveys shall be fully indexed and kept in securely bound notebooks.  The notes shall be uniform in character and recorded in such a manner as to be easily and correctly interpretable by anyone having a knowledge of surveying.  There shall be no erasures; rejected readings shall have a line drawn through them with the replacement or corrected data written beside or above the original entry. In addition, each page of field notes shall contain the Project designation, the names of the survey crew personnel, the date of the survey, a brief description of weather conditions, and a record of the field book number and page number.

The field notes shall contain a description and identifying number of the equipment employed, the rod type, a reading of the atmospheric pressure as needed, prism constants, and all other parameters and attributes having a significant effect on the results of survey work.

The field notes shall contain descriptions and sketches of the existing primary control used for origin and closure as well as for data on the primary and supplemental control of the entire Project.  The results of the primary control survey(s) executed by the Contractor shall be accurately tabulated and adjusted to conform to the requirements specified by the NJDOT under Section 4-04.1 and Section 4-04.2.  These notes shall be subsequently transferred on to reproducible sheets for inclusion in the control report.

Upon completion of the work, the Contractor shall forward all field notes and all computation and adjustment sheets to the NJDOT, and shall become the property of NJDOT.

4-08.2  Control Report

The Contractor shall prepare and furnish to the NJDOT two (2) bound copies of a control report containing all the pertinent data on primary control for the Project.  The control report shall be prepared on 210 MM x 297 MM sheets and shall consist of a narrative section, a copy of the computation and adjustment sheets, the descriptions and sketches of all control points and their field ties together with references to the control network for the entire Project, and a control diagram index drawn approximately to scale and covering the entire project in a single overview.

The original computations and adjustments and the original descriptions and sketches shall be prepared on 210 MM x 297 MM sheets and furnished to the NJDOT in a separate bound report.  All control points, traverses, observations and field data shall be in a computer format that is compatible with NJDOT software.

  1. Narrative:  The narrative section shall clearly and concisely report on the existing primary control utilized for the origin and closure of each primary traverse and level circuit established by the Contractor.  A clear explanation shall also be provided covering the methods used to produce the Project primary control survey in conjunction with the closure ties, the actual closures achieved, and the manner in which the closure errors were distributed within the adjustments.  Relevant details shall be correlated with the control diagram and the information contained therein where appropriate.
  2.  

  3. Control Diagram:  The control diagram shall complement the narrative section of the control report.  It shall be prepared to a scale no smaller than one to twenty four thousand (1:24 000) and shall show clearly the arrangement of existing primary controls as well as the primary controls for the project.

     

    The control diagram may be rendered on an existing topographic or other key map as a base plan for plotting each control point, or it may be prepared separately as a sketch.  The control diagram shall consist of the following:

     

    1. Where applicable, the actual boundaries of the separate map sheets shall be drawn on the control diagram and referenced thereon according to the map sheet numbers assigned to them for the Project.
    2.  

    3. The existing primary control points situated in or accessibly near the Project area and recovered for use as origin and closure points.
    4.  

    5. All azimuth marks and their locations, as well as all station markers and bench marks used to establish any and all traverses, triangulation and trilateration nets, and all bench marks and level circuits
    6. An appropriate title and legend for the Project designation, a north arrow showing the direction of orientation of the control diagram, the symbols used, and a graphic scale applicable to the control diagram.

     

  4. Computations:  The coordinates of each point shall be reported in the system and datum for the project, either New Jersey State Plane Coordinate system, or North American 1988 Datum.  Reduction, correction, closure and adjustment computations of each traverse surveyed shall include:

     

    • Verification that azimuth closure specifications are met in accordance classifications and accepted standards of accuracy contained in Table 4-1.
    •  

    • Correction of angles for systematic error.  The azimuth closure errors may be distributed evenly or by weighted least squares computation.
    •  

    • Verification that position closure specifications are met (using corrected angles), in accordance to accepted classifications and standards of accuracy in Table 4-1. Specifications must be met computing both from start to end and from end to start.
    •  

    • Field distances (EDM measurements) shall be converted to Grid distances by multiplying by the combined scale factor and sea level (Elevation) factor.  Plane traverses may be adjusted by any of the standard adjustment methods.
    •  

    • The control report shall include a tabulation of the Plane Coordinates of each survey station before traverse adjustments and after traverse adjustments.

4-09     GLOBAL POSITIONING SURVEYING SYSTEM

4-09.1  General

One of the modern methods of establishing Geodetic Control for Photogrammetric mapping is the Global Positioning System (GPS). GPS Satellite Surveying is a three-dimensional measurement system based on observations of the radio signals of the NAVSTAR  Global Positioning System.  The GPS observations or data gathered are processed to determine station positions in Cartesian coordinates (x, y, z), which can be converted to geodetic coordinates(Latitude and longitude, and height-above reference ellipsoid).  With adequate connections to vertical control network points and determination of the height of the geoid, orthometric heights or elevations can be computed for the points with unknown elevations.  GPS provides higher accuracy with shorter observation time than other surveying systems.

Following are excerpts taken from the Federal Geodetic Control  Committee (Appendix A) Charting and Geodetic Services published preliminary document, entitled Geometric Geodetic Accuracy Standards and Specifications For Using Relative Positioning Techniques, Version 5.0, May 11, 1988 and reprinted with corrections August 1, 1989.  This is not a final document but could be used as a guideline for the planning and execution of geodetic surveys using GPS Relative Positioning Techniques.

The specifications in this document are presently limited to fixed or static mode of relating positioning survey operations.  In the static mode receiver/antennas are not moving while data is being collected.  Future versions of this document will include specifications for kinematic modes of operation where one or more receiver/antennas are moving (possibly stopping only briefly at survey points) while one or more other receivers are continuously collecting data at fixed locations.

4-09.2  GPS Survey Standards And Specifications

Survey Standards are defined as minimum accuracies that are necessary to meet specific objectives, while Specifications are defined as field methods required to meet a particular standard.

  1. GPS Survey StandardsTable 4-4 shows the Geometric Relative Positioning Accuracy Standards for three-dimensional Surveys using space system techniques.

     

    Assumptions and Criteria used in the development of GPS Accuracy Standards:
  2.  

     

  3. Network Design & Geometry SpecificationsTable 4-5 summarizes the specifications for the network design and connection factors, including minimum station spacing, ties to existing horizontal and vertical network control points and direct connection requirements.

     

    Table 4-6 summarizes the minimum spacing between station-pairs for corresponding to relative position accuracies possible achieved from a GPS survey for a range of azimuth accuracy standards.
  4.  

  5. Instrumentation Specifications:
  6.  

     

  7. Calibration Specifications:  The field calibration consists of testing the GPS equipment performance and the associated baseline processing software on a three-dimensional test network.
  8.  

  9. The three-dimensional test network should be composed of four or more stations spaced approximately 50 meters to 10 kilometers apart.
  10.  

     

  11. Field Survey Procedures:  The precision of the GPS vector baseline results depends on the number of satellites visible simultaneously from each station during an observing session, their geometric relationships, duration of the period when the desired number of satellites can be observed simultaneously, the uncorrected effects of ionospheric and tropospheric refraction, and the line length.  See Appendix G for examples of geometric survey statistics.

     

    Table 4-7 summarizes the field procedures that should be allowed to achieve the desired accuracy standards.  These field procedures are valid only for relative positioning surveys and are subject to change as more satellites become available and processing techniques  are refined.
  12.  

    Factors that affect the results are:

     

     

  13. Office Procedure Specifications:  Criteria for processing and determining the quality of GPS relative positioning results are as follows:
  14.  

    1. The cutoff angle for data points should be no greater than 20°.
    2.  

    3. The point position (absolute) coordinates for the station held fixed in each single, session or network baseline solution must be referenced to the datum for the satellite orbital coordinates (ephemerides).  This datum is now called the World Geodetic System 1984 (WGS-84)  (DMA 1987).

       

      In order of descending accuracies, the following are acceptable methods of estimating the fixed coordinates:
    4.  

      (a)               Point position reduction of the GPS observations using Doppler smoothed pseudorange (Code Phase) measurements.

      (b)               Point position coordinates determined from unsmoothed GPS pseudorange measurements.

      (c)               Point position reduction of Transit Doppler observations using the precise ephemerides and transformed to WGS-84.

      (d)               Use of NAD 83 published coordinates.

      (e)               Transformation of coordinates in a non-geocentric datum    (e.g. NAD 1927) to the WGS-84 datum.  In this method, the surveyor must be careful in obtaining transformation values that reflect with sufficient accuracy the differences between the non-geocentric local datum and the WGS-84 system.

       

    5. Processing must account for the offset antennae phase center relative to the station mark in both horizontal and vertical components.
    6.  

    7. As a rule of thumb, the number of simultaneous phase observations rejected (excluding those affected by cut-of angle and non-simultaneous observations) for a solution should be less than 5 percent for accuracy standards AA, A and B,  and 10 percent for the remaining standards.
    8.  

    9. Depending on the number of observations, quality of data, method of reduction, and length of base lines, the standard deviation of the range residuals in the base line solution should be between 0.1 and   2 CM for orders A, B, and 1; 1 to 4 CM for order 2; and, 1 to 8 CM for order 3.
    10.  

    11. The maximum allowable formal standard errors for the baseline components may depend on the particular software.  With proper weighting in a fixed orbit solution the values should be less than the expected accuracy for the orbit data.  Typically this range within 2 CM for base lines with lengths at less than 50 KM.

     

  15. Analysis & Adjustments:  In practice, there will be two classifications for a GPS relative positioning survey. One would be based on the internal consistency of the GPS network adjusted independently  of the local network control.  This would be called the "geometric" classification. The second  classification,  if required, would  be  based on  the results of  a constrained adjustment where stations of the GPS survey network connected to the local network control are held fixed to vertical and horizontal coordinates in the "National Geodetic Reference System(NAVD 1988 and NAD 1983).  This is referred to as the "NGRS" classification. Table 4-8 summarizes the specifications to aid in classifying the results for a GPS survey project.

     

    Loop closures and differences in repeat base line measurements will be computed to check for blunders and to obtain initial estimates for the internal consistency of the GPS network.  Error of closure is the ratio of the length of the line representing the equivalent of the resultant errors in the base line vector components to the length of the perimeter of the figure constituting the survey loop analyzed.  The error of closure is valid for orders A and B surveys only when there are three or more independently determined base lines (from three or more observing sessions) included in the loop closure analysis.  For orders 1 and lower, independently determined baselines from a minimum of two observing session (simultaneous observations) are not valid for analyzing the internal consistency of the GPS survey network.

     

    After adjusting for any blunders, a minimally constrained (sometimes called a free least squares adjustment should be performed and the normalized residuals examined.

     

    The normalized residual is the residual multiplied by the square root of its weight, i. e. the ratio of the residual to the a priori standard error. Examining the normalized residuals helps to detect bad base line vectors.  In the "free" adjustment, one arbitrary station is held fixed in all three coordinates and the four bias unknowns(3 rotations and one scale parameter) are set to zero values (Vincenty 1987).  The observation weights should be verified as realistic by inspecting the estimate of the variance of unit weight, which would be close to 1. However, in practice, it may be higher, perhaps in the range of 3 to 5 because for a particular GPS baseline solution software, the formal errors from the base line solutions may be too optimistic.

     

    Vector component (relative position) standard errors computed by error propagation between points in a correctly weighted minimally constrained least square adjustment will indicate the maximum achievable precision for the "geometric" classification. The constrained least squares adjustment will use models which account for: the reference ellipsoid for the network control, the orientation and scale differences between the satellite and network control datum's, geoid-ellipsoid relationships,  the distortions and/or reliability in the network control , and instability in the control network due to horizontal and/or vertical deformation. A survey variance factor ratio  will be computed to aid  in  determining  the  "NGRS"  classification  of  the adjustment.  The classification for the adjustment into the NGRS should not exceed the order for the combined control network.

     

    The constrained adjustment determines the appropriate orientation and scale corrections to the GPS Base line vectors so it will conform to the local network control.  Because of possible significant inconsistencies in the network control between sections of the project area, it may be necessary  to compute several sets of orientation and scale corrections.  This is done by dividing the project area into smaller "bias groups" , provided that in each such group there is sufficient existing control with adequate distribution that is tied to the GPS network (Vincenty 1987).

     

    If reliable geoid height data are available, the adjustment to determine elevations should be done in terms of heights above the ellipsoid.  However useful estimates for elevations above mean sea level can be determined if geoidal height data are not available by fixing in an adjustment at least three stations with elevations.  The stations with elevations must be well-distributed to permit fitting a plane through the three heights. The effect of ignoring the slope means that the geoidal slope is absorbed by two rotation angles(around the north and east axes in a horizon system) and geoidal heights are absorbed by the scale correction in a constrained 3-D adjustment (Vincenty).  If there is one or more significant changes in the geoidal slope within the project area, the project can be divided into smaller "bias groups", provided there is at least three vertical control stations appropriately distributed within the "bias group" area.

     

    The discussion related to "bias group" points out the importance in the planning for a GPS survey project to insure there is included in the survey adequate connections to the horizontal and vertical control network.

Table 4-4:       Geometric Relative Positioning Accuracy Standards for Three-Dimensional Surveys Using Space System Techniques

 

 

(95 PERCENT CONFIDENCE LEVEL)

 

 

MINIMUM GEOMETRIC

ACCURACY STANDARD

SURVEY CATEGORIES

ORDER

BASE

ERROR

LINE-LENGTH

DEPENDENT ERROR

 

 

e

(cm)

p

(ppm)

a

(1:a)

Global-regional geodynamics; 

 

 

 

 

 

deformation measurements

AA

0.3

0.1

1:100 000 000

National Geodetic Reference System,

 

 

 

 

 

“primary” networks; regional-local geodynamics;  deformation measurements

 

 

A

 

 

0.5

 

 

0.1

 

 

1:10 000 000

National Geodetic Reference System,

 

 

 

 

 

“secondary” networks; connections to the “primary” NGRS network; local geodynamics; deformation measurements; high-precision engineering surveys

 

 

 

 

B

 

 

 

 

0.8

 

 

 

 

1

 

 

 

 

1:1 000 000

National Geodetic Reference System

 

 

 

 

 

(Terrestrial based); dependent control surveys to meet mapping, land information, property, and engineering requirements

 

(C)

 

1

2-I

2-II

3

 

 

 

1.0

2.0

3.0

5.0

 

 

 

10

20

50

100

 

 

 

1:100 000

1: 50 000

1: 20 000

1: 10 000

Note:  For ease of computation and understanding, it is assumed that the accuracy for each component of a vector base line measurement is equal to the linear accuracy standard for a single-dimensional measurement at the 95 percent confidence level.  Thus, the linear one-standard deviation (s) is computed by:

                                                    _____________

                                      s = + [Öe2 + (0.1d.p) 2 ] / 1.96.              (See Appendix B)

 

Where, d is the length of the baseline in kilometers.                                                                                          5-26-88

(GLOBAL POSITIONING SYSTEM (GPS) Standards and Specifications By the Federal Geodetic Control Committee (Version # 5.0).  Reprint.)


Table 4-5:       Guidelines for Network Design, Geometry and Connections

 

GROUP

AA

A

B

C

GEOMETRIC ACCURACY

ORDER

AA

A

B

1,2-I&II,3

STANDARDS

ppm

0.01

0.1

1.0

10,20,50,100

 

BASE (cm)

0.3

0.5

0.8

1   2   3   5

Horizontal network control of NGRS(a), minimum number of stations

 

 

 

 

 

When connections are to orders AA, A or B

4

3

3

2

 

When connections are to order 1

nab

nab

nab

3

 

When connections are to orders 2 or 3

nab

nab

nab

4

Vertical network control of NGRS(a), minimum number of stations (c)(d)

 

5

 

5

 

5

 

4

Continuous tracking stations (master or fiducials), minimum number of stations

 

4

 

3

 

2

 

op

Station Spacing (KM)

 

 

 

 

 

Between “existing network control” and CENTER of project:

 

 

 

 

 

Not more than

110d

10d

7d

5d

 

50 percent not less than

Ö5d

Ö5d

Ö5d

d/5

 

Between “existing network control” located outside of project’s outer boundary and the edge of the boundary, not more than

 

 

3000

 

 

300

 

 

100

 

 

50

Location of network control

 

 

 

 

 

(relative to center of project); number of “quadrants”, not less than

 

4

 

4

 

3

 

3

Direct connections should be performed, if practical, between

 

 

 

 

 

Any adjacent stations (new or old, GPS or non-GPS) located near or within project area, when spacing is less than (KM)

 

 

30

 

 

30

 

 

10

 

 

5

Legend:

d        -

 

NGRS -

CL      -

na      -

op      -

is the maximum distance in (KM) between the center of the project area and any station of the project.

National Geodetic Reference System

Confidence level

not applicable

optional                                                                                                              4-17-89

Note:

If it is not practical to plan a survey that is within the criteria, minor adjustments may be provided that it is authorized by the agency requesting the survey.

Remarks:

a)       Consult National Geodetic Survey officials whenever it is necessary to consider exceptions to these criteria, particularly, when the GPS survey project data are to be submitted to NGS for incorporation in the NGRS.

b)       If a survey with an accuracy standard of AA, A, or B is specified and one objective in the survey is to upgrade the existing network, then connections to a minimum of four stations are required or at least one station in each one-degree block with a minimum of four stations.

c)       First choice is vertical network control established and/or maintained by the Natioanl Geodetic Survey.  When it is not possible to occupy the minimum number of NGRS points, non-NGRS control points may be used.  This should be documented in the project report.

d)       If it is expected that the constrained adjustment for determination of the elevations within the project area will be based on more than one “bias group” (see discussion under section on Office procedures, Analysis and Adjustments) then the minimum number of stations specified is that which is required within the area for each “bias group”.  For example, if there two bias groups and ties required to four bench marks, then four bench marks will be incorporated within each area of the “bias group” for a total of 8 bench marks.

5-09-88

(GLOBAL POSITIONING SYSTEM (GPS) Standards and Specifications By the Federal Geodetic Control Committee (Version # 5.0).  Reprint.)


Table 4-6:       Guidelines for Minimum Spacings for Establishing Pairs of Intervisible Stations to Meet Azimuth Reference Requirements

SPACING BETWEEN A “PAIR” OF STATIONS,

AZIMUTH ACCURACY REQUIRED IN SECONDS OF ARC

(95 PERCENT CONFIDENCE LEVEL

NOT LESS THAN

1

2

4

6

10

 

(METERS)

GPS RELATIVE POSITION PRECISION (MM)

(95) PERCENT CONFIDENCE LEVEL)

100

-

-

2

3

5

200

-

2

4

6

10

300

-

3

6

9

14

400

2

4

8

12

19

500

3

5

10

14

24

600

3

6

12

18

29

Example:

If the expected relative position precision from a GPS survey between two marks spaced less than 1 000 meters apart is 2 MM at the 95 percent confidence level, then to achieve an azimuth accuracy of 2 seconds at the 95 percent confidence level, the minimum spacing between the pair of stations is 200 meters.                                                                                                                                1-01-86

(GLOBAL POSITIONING (GPS) Standards and Specifications By the Federal Geodetic Control Committee. (Version # 5.0).  Reprint.)


Table 4-7:       Guidelines for GPS Field Survey Procedures

 

GROUP

AA

A

B

C

GEOMETRIC RELATIVE

ORDER

AA

A

B

1,2-I&II,3

POSITIONING STANDARDS

ppm

0.01

0.1

1.0

10,20,50,100

Two frequency observations (1 and L2) required(a)

 

 

 

 

 

Daylight observations (b)

Y

Y

Y

op

Recommended number of receivers observing simultaneously, not less than

5

5

4

3

Satellite Observations

 

 

 

 

 

RDOP values during observing session (meters/cycle)(d)

[TO BE ADDED IN FUTURE VERSION]

 

Period of observing session (observing span), not less than (min):

 

 

 

 

 

[4 or more simultaneous satellite observations](e)

 

 

 

 

 

Triple difference processing(f)

na

na

240

60-120

 

Other processing techniques(g):

 

 

 

 

 

General requirements(b)(i)

240

240

120

30-60

 

Continuous and simultaneous between all receivers, period not less than (i)(j)

 

180

 

120

 

  60

 

20-30

 

Data sampling rate - maximum time interval between observations (sec)

15

30

30

15-30

 

Minimum number of quadrants from which satellite signals are observed

4

4

3

3 or 2(k)

 

Maximum angle above horizon for obstructions(v) (degrees)

10

15

20

20-40

Independent occupations per station (1)

 

 

 

 

 

Three or more (% of all stations, not less than)

80

40

20

10

 

Two or more (% of stations, not less than):

 

 

 

 

 

New stations

100

80

50

30

 

Vertical control stations

100

100

100

100

 

Horizontal control stations

100

75

50

25

 

Two or more for each station of “station-pairs”(M)

Y

Y

Y

Y

Master of fiducial stations (n)

 

 

 

 

 

Required, yes or no (o)

Y

Y

Y

op

 

If yes, minimum number

4

3

2

 

Repeat base line measurements

 

 

 

 

 

about equal number in N-S and E-W directions, minimum not less than (percent of total independently [nontrivial] determined base lines).

25

15

5

5

Loop closure requirements when forming loops for post-analyses

[NOTE:  Also, see Table 4-8]

 

 

 

 

 

Base lines from independent observing sessions, not less than

3

3

2

2

 

Base lines in each loop, total not more than

6

8

10

10

 

Loop length, generally not more than (KM)

2 000

300

100

100

 

Base lines not meeting criteria for inclusion in any loop, not more than [percent of all independent nontrivial lines (p)]

 

0

 

5

 

20

 

30

 

Stations not meeting criteria for inclusion in any loop, not more than (percent of all stations)

 

0

 

5

 

10

 

15

Direct connections are required

 

 

 

 

 

Between ANY adjacent (NGRS and/or new GPS) stations (new or old, GPS or non-GPS) stations or within project area, when spacing is less than (KM)

 

30

 

10

 

5

 

3

Antenna setup

 

 

 

 

 

Number of antenna phase center height measurements per session, not less than

 

3 (q)

 

3 (q)

 

2

 

2

 

Independent plumb point check required (r)

Y

Y

Y

op

Photograph (closeup) and/or pencil rubbing

 

 

 

 

 

required for each mark occupied

Y

Y

Y

Y

Meteorological observations

 

 

 

 

 

Per observing session, not less than

3 (s)

3 (s)

2 (t)

2 (t) or op

 

Sampling rate (measurement interval), not more than (min)

30

30

60

60

Water vapor radiometer measurements required

 

 

 

 

 

at selected stations?

op

op

N

N

Frequency standard warm-up time (hr) (u)

 

 

 

 

 

Crystal

12

12

(u)

(u)

 

Atomic

1

1

(t)

(t)

(GLOBAL POSITIONING SYSTEM (GPS) Standards and Specifications By the Federal Geodetic Control Committee (Version # 5.0).  Reprint.)

Table 4-7:       Guidelines for GPS Field Survey Procedures (cont.)

Legend:

nr - not required, na - not applicable, op - optional

Remarks:

(a)     If two-frequency observations can not be obtained, it is possible that an alternate method for estimating the ionospheric refraction correction would be acceptable, such as modeling the ionosphere using two-frequency data obtained from other sources.  Or, if observations are during darkness, single frequency observations may be acceptable depending on the expected magnitude of the ionospheric refraction error.

(b)     When spacing between any two stations occupied during an observing session is more than 50 KM, two frequency observations may need to be considered for Accuracy Standards of Order 2 or higher

(c)     Multiple baseline processing techniques.

(d)     Studies are underway to investigate the relationship of Geometric Dilution of Precision (GDOP) values to the accuracy of the base line determinations.  Initial results of these studies indicate there is a possible correlation.  It appears the best results may be achieved when the GDOP values are changing in value during the observing session.

(e)     The number of satellites that are observed simultaneously cannot be less than the number specified for more than 25 percent of the specified period for each observing session.

(f)      Absolute minimum criteria is 100 percent of specified period.

(g)     “Other” includes processing carrier phase data using single, double, nondifferencing, or other comparable precise relative positioning processing techniques.

(h)     The times for the observing span are conservative estimates to ensure the data quantity and quality will give result that will meet the desired accuracy standard.

(i)        

(j)       Absolute minimum criteria for the data collection observing span is that period specified for an observing session that includes continuous and simultaneous observations.  Continuous observations are data collected that do not have any breaks involving all satellites; occasional breaks for individual satellites caused by obstructions are acceptable, however, these must be minimized.  A set of observations for each measurement epoch is considered simultaneous when it includes data from at least 75 percent of the receivers participating in the observing session.

(k)      Satellites should pass through quadrants diagonally opposite of each other.

(l)       Two or more independent occupations for the stations of a network are specified to help detect instrument and operator errors.  Operator errors include those caused by antenna centering and height offset blunders.  When a station is occupied during two or more sessions, back to back, the antenna/tripod will be reset and replumbed between sessions to meet the criteria for an independent occupation.  To separate biases caused by receiver and/or antenna equipment problems from operator induced blunders, a calibration test may need to be performed.

(m)    Redundant occupations are required when pairs of intervisible stations are established to meet azimuth requirements, when the distance between the station pair is less than 2 KM, and when the order is 2 or higher.

(n)     Master or fiducial stations are those that are continuously monitored during a sequence of sessions, perhaps for the complete project.  These could be sites with permanently tracking equipment in operation where the data are available for use in processing with data collected with the mobile units.

(o)     If simultaneous observations are to be processed in the session or network for base line determinations while adjusting one or more components of the orbit, then two or more master stations shall be established.

(p)     For each observing session there are r-1 independent base lines where r is the number of receivers collecting data simultaneously during a session, e.g. if there were 10 sessions and 4 receivers used in each session, 30 independent base lines would be observed.  (see Appendix F)

(q)     A measurement will be made both in meters and feet, at the beginning, mid-point, and end of each station occupation.

(r)      To ensure the antenna was centered accurately with the optical plummet over the reference point on the marker, when specified, a heavy weight plumb bob will be used to check that the plumb point is within specifications.

(s)     Measurements of station pressure (in millibars), relative humidity, and air temperature (in °C) will be recorded at the beginning, midpoint, and end depending on the period of the observing session.

(t)       Report only unusual weather conditions, such as major storm fronts passing over the sites during the data collection period.  This report will include station pressure, relative humidity, and air temperature.

(u)     The amount of warm-up time required is very instrument dependent.  It is very important to follow the manufacturer’s specifications.

(v)     An obstruction is any object that would effectively block the signal arriving from the satellite.  These include buildings, trees, fences, humans, vehicles, etc.

(GLOBAL POSITIONING SYSTEM (GPS) Standards and Specifications By the Federal Geodetic Control Committee (Version # 5.0).  Reprint.)

Table 4-8:       Office Procedures for Classifying GPS Relative Positioning Networks Independent of Connections to Existing Control

GEOMETRIC RELATIVE

Order

AA

A

B

1

2-I

2-II

3

POSITIONING STANDARDS

ppm

0.01

0.1

1.0

10

20

50

100

Ephemerides

 

 

 

 

 

 

 

 

Orbit accuracy, minimum (ppm)

0.008

0.05

0.5

5

10

25

50

 

Precise ephemerides required?.

Ya

Ya

Y

op

op

N

N

Loop closure analyses (b)

 

 

 

 

 

 

 

 

When forming loops, the following are minimum criteria:

 

 

 

 

 

 

 

 

Base lines in loop from independent observations not less than

4

3

2

2

2

2

2

 

Base lines in each loop, total not more than

6

8

10

10

10

15

15

 

Loop length, not more than (KM)

2 000

300

100

100

100

100

100

 

Base lines not meeting criteria for inclusion in any loop, not more than (percent of all independent lines)

0

0

5

20

30

30

30

 

In any component (X, Y, Z), “maximum” misclosure not to exceed (CM)

10

10

15

25

30

50

100

 

In any component (X, Y, Z), “maximum” misclosure, in terms of loop length, not to exceed (ppm)

0.2

0.2

1.25

12.5

25

60

125

 

In any component (X, Y, Z), “average” misclosure, in terms of loop length, not to exceed (ppm)

0.09

0.09

0.9

8

16

40

80

Repeat base line differences

 

 

 

 

 

 

 

 

Base line length, not more than (KM)

2 000

2 000

500

250

250

100

50

 

In any component (X, Y, Z), “maximum” not to exceed (ppm)

0.01

0.1

1.0

10

20

50

100

Minimally constrained adjustment analyses

[TO BE ADDED IN FUTURE VERSION]

Remarks:

(a)     The precise ephemerides is presently limited to an accuracy of about 1 ppm.  By late 1989, it is expected the accuracy will improve to about 0.1 ppm.  It is unlikely orbital coordinate accuracies of 0.01 ppm will be achieved in the near future.  Thus to achieve precisions approaching 0.01 ppm, it will be necessary to collect data simultaneously with continuous trackers or fiducial stations.  (see criteria for field procedures, Table 4-7.)  Then the all data is processed in a session or network solution mode where the initial orbital coordinates are adjusted while solving for the base lines.  In this method of processing the carrier phase data, the coordinates at the continuous trackers are held fixed.

(b)     Between any combination of stations, it must be possible to form a loop through three or more stations which never passes through the same station more than once.

(GLOBAL POSITIONING SYSTEM (GPS) Standards and Specifications By the Federal Geodetic Control Committee (Version # 5.0).  Reprint.)


FIGURE 4-1:   BRONZE DISK

FIGURE 4-2:   CYLINDRICAL CONCRETE MONUMENT

FIGURE 4-3:   DISK ON ROD

FIGURE 4-4:   NGS 3-D MARKER

FIGURE 4-5:   GEOMETRIC RELATIVE POSITIONING ACCURACY STANDARDS MAXIMUM ALLOWABLE ERROR AT 95% CONFIDENCE LEVEL