3　Basic Provisions

3.1　Survey

3.1.1　Aerial photographing and satellite positioning shall be made full use of in the survey，and other new survey technologies shall be actively promoted.The survey results obtained using new survey technologies shall satisfy the applicable precision requirements given in this code.

3.1.2　China Geodetic Coordinate System 2000，Xi an Geodetic Coordinate System 1980 or Beijing Geodetic Coordinate System 1954 should be used as the coordinate systems for the survey，and Huanghai Vertical Datum 1956 or National Vertical Datum 1985 should be used as the elevation system.Uniform horizontal and elevation systems shall be used for the survey at the feasibility study stage，preliminary design stage and detailed design stage.Projection deformation shall be taken into account for selection of central meridian，and the permissible deviation of projection deformation shall not exceed 5cm/km.

3.1.3　The survey scope of plans shall be 50m on both sides of the centerline for 330kV，±400kV，500kV and±500kV overhead transmission lines，and 75m for±660kV and 750kV overhead transmission lines.

3.1.4　The survey results submitted shall include drawings and corresponding electronic documents.Data interfaces should be provided between the software used and the software for line design.Field collected raw data shall be maintained.

3.1.5　Where a total station or theodolite is used for direct route location，the allowed deviation of horizontal angle of straight-line stake positions shall be 180°±1′.The relative error of the discrepancy of two observation sets shall not be larger than 1/1000.When using GPS to locate the route or adjacent straight-line stakes or tower location stakes，the root mean square error（RMSE）of relative coordinates shall not exceed 0.05m，and the error of relative elevation difference for adjacent straight-line stakes or tower location stakes shall not exceed 0.3m.

3.1.6　When using GPS for connection surveying of horizontal coordinates or surveying of photo control points，the rapid static mode or static mode should be adopted.When using GPS for survey of plans and sections，crossing-over plans，topographic maps，and setting out survey of tower location stakes and straightline stakes，the real-time dynamic mode or semi-dynamic mode should be adopted.The ellipsoid selected for GPS survey shall have uniform basic parameters throughout different stages of the same project.

3.1.7　The reference station for GPS survey of straight-line stakes shall be located in an open area with sparse vegetation，convenient traffic，and convenient conditions for GPS receiving.The reference station shall survey the coordinates and elevations in the rapid static mode or static mode.A permanent stake shall be buried at the GPS reference station.

3.1.8　A unique heading direction shall be determined for one line.Relative positions of"left"and"right"shall be based on the determined heading direction.The cumulative distances and stake numbers shall be incremental along the heading direction.

3.1.9　The methods，instruments and procedures of surveying shall be selected based on the terrain，landform and vegetation.

3.1.10　The precision requirements for Class I，Class II and Class III distance measuring instruments shall be in compliance with the provisions on precision grading in GB/T 16818 Specifications for Short to Medium Ranges Electro-optical Distance Measurements.The theodolites of grades DJ1，DJ2 and DJ6 and their basic technical parameters shall comply with the provisions in the current national standard GB 3161 The Series of Theodolite and Basic Parameters.The levellers of grades DS1，DS3 and DS10 and their basic technical parameters shall comply with the provisions in the national standard in force GB 3160 The Series of Level and Basic Parameters.