6.5　Horizontal and Elevation Connection Survey

6.5.1　Where the lines are close to or run through planning areas，industrial and mining areas，military installation areas，signal transceiver stations，and historic preservation areas，connection survey shall be carried out for the horizontal coordinates if uniform horizontal coordinate systems are required in relevant agreements.

6.5.2　In horizontal connection survey，the RMSE precision tolerance of the center point position of an angle tower shall not be 0.6mm more than that of the map used for areas on which relevant agreements are reached.

6.5.3　The starting and ending points of ingoing and outgoing lines of a substation or power plant shall be set out by using a coordinate system consistent with that used by the substation or power plant.The coordinates after location survey shall be converted to a coordinate system consistent with that of the line project.

6.5.4　Where the lines run through rivers，lakes，reservoirs，waterway networks and waterlogging areas，the surveyors shall carry out connection survey for the elevations of flood marks and flood water levels according to the hydrological investigation needs.

6.5.5　For the connection survey of elevation，if the line length is in the range of 0-5km，a minimum of Class II photoelectric distance measurement trigonometric leveling shall be used，if the line length is in the range of 5-10km，a minimum of Class I photoelectric distance measurement trigonometric leveling or mapping leveling shall be used，and if the line is more than 10km long，Class IV leveling or Class IV photoelectric distance measurement trigonometric leveling shall be used.

6.5.6　For Class I and Class II photoelectric distance measurement trigonometric leveling，the precision for measuring the heights of instruments and collimated objects shall not be more than 5mm.The calculated vertical angles shall be rounded up to 1 second，and the calculated elevations to 1 millimeter.The median（rounded up to 1 centimeter）shall be taken as the final result.The elevation differences calculated shall be corrected in terms of earth curvature and atmospheric refraction error.The precision requirements for Class I and Class II photoelectric distance measurement trigonometric leveling shall be in compliance with the provisions in Table 6.5.6-1.The technical requirements for mapping leveling shall conform to the provisions in Table 6.5.6-2.

Table 6.5.6-1　Precision requirements for photoelectric distance measurement trigonometric leveling

Note:S—length of measured legs，km；n—number of measured legs.

Table 6.5.6-2　Precision requirements for mapping leveling

Note:S—length of line，km，n—number of observation stations.

6.5.7　For Class IV photoelectric distance measurement trigonometric leveling，the precision for measuring the heights of instruments and collimated objects shall not be more than 1mm.The calculated vertical angles shall be rounded up to 1 second，and the calculated elevations to 1 millimeter.The median（rounded up to 1 millimeter）shall be taken as the final result.The elevation differences calculated shall be corrected in terms of earth curvature and atmospheric refraction error.The main technical requirements for Class IV photoelectric distance measurement trigonometric leveling shall conform to the provisions in Table 6.5.7-1 and Table 6.5.7-2.

The main technical requirements for Class IV mapping leveling shall conform to the provisions in Table6.5.7-3 and Table 6.5.7-4.

Table 6.5.7-1　Precision requirements for Class IV photoelectric distance measurement trigonometric leveling

Note:S—length of measured legs，km.

Table 6.5.7-2　Precision requirements for Class IV photoelectric distance measurement trigonometric leveling

Table 6.5.7-3　Precision requirements for Class IV mapping leveling

Note:S—length of line，km，n—number of observation stations.

Table 6.5.7-4　Precision requirements for Class IV leveling observation