6.4　Survey of Stake Spacing and Elevation Difference

6.4.1　The survey of stake spacing and elevation difference may be combined and carried out simultaneously with routing survey.Both geodimeter and GPS may be used for the survey of stake spacing and elevation difference.

6.4.2　Where a geodimeter is used for surveying the stake spacing and elevation difference，two observation sets in opposite directions should be made or the heights of instrument and observation marker may be changed to make two sets of observation in the same direction.Distance measurement shall comply with the following provisions:

1　The sketch of stake position relationship shall be developed for each observation station.

2　Observation for each observation set shall be carried out respectively in opposite directions.For each observation set，the data shall be surveyed twice.All data shall be recorded in automatic or manual way，and the readings and records shall be checked in time.

3　When measuring in the same direction，two observation sets shall be made with the survey data obtained twice for each set.The requirements shall be the same as those for observation in opposite directions，but the prism height or instrument height shall be changed for the second observation set.

4　The relative error of distance discrepancy for two observation sets shall be less than 1/1000.If the above limit is exceeded，an additional observation set shall be made and the results of two satisfactory observation sets shall be selected.Otherwise，the survey shall be made for two new observation sets.

6.4.3　The use of geodimeter shall satisfy the following requirements:

1　The specifications and operational procedures in the instructions of the instrument shall be complied with.

2　Conversation with interphone shall be suspended during work.

3　When the instruments are erected，the survey station and lens station shall be always attended.

4　If two lens stations are at the same height of collimation line，the prism of another station shall be arranged after one station is surveyed and determined.It is forbidden to align two prisms with the distance measurement instrument.

5　It is forbidden to align the tripod head with the sun.

6.4.4　Elevation survey shall be carried out simultaneously with distance measurement.Trigonometric leveling shall be used for the elevation difference survey with two observation sets.

The discrepancy of elevation difference surveyed in two observation sets shall not be more than 0.4S（m）（S is the length of leg in km.If S is less than 0.1km，it shall be taken as 0.1km）.The heights of instrument and prism shall be both measured rounding up to centimeters，and the mean of elevation differences obtained from two observation sets shall be taken as the final results，rounded up to decimeters.

6.4.5　If the distance exceeds 400m，the elevation difference shall be corrected in terms of the earth curvature and atmospheric refraction error using the following formula:

Where:

R——mean radius of the earth curvature，m；

S——Leg length，m；

K——Coefficient of atmospheric refraction error.

6.4.6　If the discrepancy of elevation difference exceeds the limit，one additional observation set on the vertical angle is needed and the results of two qualified observation sets shall be taken.

6.4.7　When GPS receiver is used for surveying the stake spacing，the distance of mobile stations from the reference station shall not exceed 8km and the elevation difference between stakes shall be checked.