3.2　Satellite Positioning Survey

Ⅰ　Main Technical Requirements for Satellite Positioning Survey

3.2.1　The main technical indicators for satellite positioning survey control networks of various accuracies shall be as specified in Table 3.2.1.

3.2.2　The accuracies of baselines in control networks shall be calculated using the following formula:

Where:

σ——RMSE of baseline length（mm）；

A——Fixed error（mm）；

B——scale error coefficient（mm/km）；

d——average leg length（km）.

3.2.3　The observation accuracy of satellite positioning survey control network shall be estimated in accordance with the following requirements:

1　The RMSE of GPS network can be calculated as follows:

Where:

m——RMSE of GPS network（mm）；

N——number of non-simultaneous loops in GPS network；

n——number of legs in every non-simultaneous loop；

W——linear misclosure of non-simultaneous loop（mm）；

Wx，Wy，and Wz——X，Y，and Z misclosure components of non-simultaneous loop（mm）.

2　For the RMSE of GPS network，the accuracy requirement for the baselines in control networks at equivalent accuracy levels shall be met，and the following formula shall apply:

Ⅱ　Design，Point Selection，and Monumentation of Satellite Positioning Survey

Control Network

3.2.4　Satellite positioning survey control networks shall be arranged in accordance with the following requirements:

1　The control networks shall be designed comprehensively taking into account the actual conditions of the survey area，accuracy requirements，satellite conditions，types and number of receivers，and the existing survey data.

2　When establishing the primary control network，more than two high-level control points in national or regional coordinate system should be surveyed for correlation；the long legs in the control network should constitute geodetic quadrangle or midpoint polygon.

3　The control network shall be such that independent observation legs form one or multiple closed loops or connecting routes，and the number of such legs in the control network should not exceed six.

4　The total number of independent observation baselines in the control network should not be less than 1.5 times the number of necessary observation baselines.

5　Where necessary，densification network may be established flexibly provided that the accuracy requirements specified in this code are met.

6　For survey areas using GPS-RTK mapping technique，the distribution of reference stations shall be incorporated into the arrangement of primary network.

3.2.5　The control points shall be determined in accordance with the following requirements:

1　The control points shall be set up at hard，stable and reliable positions and allow for densification and expansion.Each control point shall have at least one intervisibility direction.

2　The control points shall be located at open field with no obstructions above the altitude angle of 15°.In the vicinity of them，there shall be neither sources that severely interfere the reception of satellite signals nor objects that strongly reflect satellite signals.

3　Use of the existing control points complying with this code is encouraged.

3.2.6　Monumentation of GPS control points shall be as specified in Appendix B，and description of GPS control points shall be as specified in Appendix C.

Ⅲ　GPS Observation

3.2.7　GPS control survey shall be performed in accordance with the basic technical requirements in Table 3.2.7.

3.2.8　Survey plans shall be prepared for large-scale GPS survey areas.

3.2.9　Prior to observation，the survey personnel shall warm up the receiver and leave it standstill and check if the battery capacity and the internal memory or available storage space of the receivers are sufficient.

3.2.10　The centering error of antenna shall not exceed 2mm and the antenna height shall be measured to the nearest 1mm.

3.2.11　During survey，use of radio communication devices near receivers shall be avoided.

3.2.12　The survey personnel shall keep a record of survey stations，including designation of control point，serial number of receiver，height of instrument and on/off time of instrument.The format of GPS survey notebook shall be as specified in Appendix D.

Ⅳ　GPS Survey Data Processing

3.2.13　The software supplied together with the receiver may be used for GPS survey data processing and baselines computation，and the following requirements shall be met:

1　The observation time required for positioning the starting point using a single receiver should not be less than 30min；

2　The computation may be performed in either single-baseline or multi-baseline mode.

3　The baseline solutions shall be double-difference ambiguity-fixed solutions.

3.2.14　All the field observation data of GPS control survey shall be checked by observing simultaneous observation loops and non-simultaneous observation loops and repeatedly observing baselines，in accordance with the following requirements:

1　The X，Y，and Z misclosure components and total loop linear misclosure of simultaneous observation loop shall be computed as follows:

2　The X，Y，and Z misclosure components and total loop linear misclosure of non-simultaneous observation loop shall be computed as follows:

3　The discrepancy between the lengths of the same baseline measured in different observations shall be computed as follows:

Where:

σ——RMSE of baseline length required for specific accuracy（mm），（see Formula 3.2.2）；

n——number of baselines of non-simultaneous loop or simultaneous loop；

W——total loop linear misclosure of non-simultaneous loop or simultaneous loop（mm），（see Formula 3.2.3-2）；

Δd——length discrepancy；

Wx，Wy，and Wz——X，Y，and Z misclosure components of non-simultaneous loop or simultaneous loop（mm）.

3.2.15　Where the GPS observation data fail to meet the checking criteria，a comprehensive analysis on the results is required.In such analysis，those incompliant baselines shall be rejected provided that the number of the remaining baselines forming non-simultaneous loops does not exceed the limit as specified in sub-clause 3 of 3.2.4.If sub-clause 3 of 3.2.4 cannot be met，the incompliant baselines or the relevant simultaneous loops shall be resurveyed.

3.2.16　After field GPS observation data are verified to meet the checking criteria，the observation accuracy of the GPS network shall be evaluated in accordance with 3.2.3.

3.2.17　The unconstrained adjustment of GPS survey control network shall comply with the following requirements:

1　Three-dimensional unconstrained adjustment shall be computed in WGS-84 coordinate system to provide the three-dimensional coordinates of each survey point in WGS-84 system，and the vector correction，length and azimuth of each baseline as well as their relevant accuracies；

2　The absolute values of corrections of baseline vectors in unconstrained adjustment shall not exceed 3 times the required RMSE of baseline length for the specific accuracy.

3.2.18　The constrained adjustment of GPS survey control network shall comply with the following requirements:

1　Two-dimensional or three-dimensional constrained adjustment shall be carried out in national or independent coordinate system.

2　For the known coordinates，distances or azimuths，forced constraint or weighted constraint is required.The relative RMSE of the leg length between constrained points shall be as specified in Table 3.2.1 for the specific accuracy.

3　The adjustment results shall include two-dimensional or three-dimensional coordinates of survey points，baseline vector corrections，baseline length and baseline azimuth as well as their relevant accuracies.Where necessary，coordinate transformation parameters and their accuracies shall also be included.

4　After constrained adjustment is made，the relative RMSE of the length of the weakest leg in control network shall meet the requirements in Table 3.2.1 for the specific accuracy.