6.2　Route Selection Survey

6.2.1　The route selection survey shall satisfy the following requirements:

1　The surveyors shall cooperate with the design personnel to survey the determined route in the field，select the angle locations of route and obtain the values of turning angles，based on the approved preliminary design route.

2　Where the lines cross over Class I and Class II communication lines，optical cables，and underground communication cables with the crossing angles less than or close to the design limits，instruments shall be used to survey the positions of lines relative to these lines or cables to obtain the values of crossing angles.

6.2.2　The total station or theodolite used for route selection shall have a precision no less than DJ6，and the precision of distance measurement of total station shall not be lower than Class III distance measurement instrument.

6.2.3　The total station or theodolite shall adopt the distance or angle center-parted method.Where the telescope in reversed direction is impossible for an electronic theodolite，one-half observation set shall be carried out on the horizontal angle in anti-clockwise direction.After direct routing，the horizontal angle shall be checked with a half observation set and recorded，and the permissible deviation of angle shall be in the range of±1.

6.2.4　When a total station or theodolite is used for route selection，directional stakes no less than 400m away from the turning angle shall be set before and after the turning angles.

6.2.5　When a total station or theodolite is used for route selection，the route map in which the positions of selected angle stakes and directional stakes are marked shall be provided appropriately for routing or location，and the angle values of angle stakes shall be provided.

6.2.6　When a digital photogrammetry system has been used for indoor route selection and the coordinates of turning angles and orthophoto maps are available，GPS shall be used for determining the route in the field.

6.2.7　When GPS is used for determining the route in the field，the coordinates and elevations of GPS control points during the GPS field control stage which have satisfactory precision and reliable stake positions shall be selected as the initial data.

6.2.8　The surveyors shall cooperate with the design personnel to survey the landform and surface features between turning angles which affect the route，during which the GPS shall be used for survey of coordinates and the positions of turning angles shall be adjusted in the field.

6.2.9　Permanent stakes should be buried when the positions of turning angles are determined.The coordinates and elevations of turning angles shall be surveyed using GPS in the real-time dynamic or rapid static mode.The RMSE of precision shall not be greater than 5cm for coordinates and not be greater than 7cm for elevation.

6.2.10　Where a total station is used for subsequent routing survey，positioning stakes shall be buried near the turning angles.Clear intervisibility shall be maintained between positioning stakes and turning stakes and the stake spacing should not be less than 80m.The coordinates and elevations of positioning stakes shall be surveyed using GPS in the real-time dynamic or rapid static mode.

6.2.11　When GPS is used for route selection or route determination，orthophoto maps in which the positions of turning angles will be provided for routing or location survey，and the surveyed coordinates and elevation values of reference station，angle stakes，and positioning stakes will also be provided.