3.3　Traverse Survey

Ⅰ　Main Technical Requirements for Traverse Survey

3.3.1　The main technical requirements for traverse survey of various accuracies shall be as specified in Table 3.3.1.

3.3.2　Where the average length of traverse legs is relatively short，the number of legs shall be limited to that obtained by dividing"Traverse Length"by"Average Traverse Leg Length"as specified in Table 3.3.1 for the specific accuracy.Where the length of traverse is less than 1/3 of that specified in Table 3.3.1，the absolute misclosure of the total traverse loop shall not exceed 13cm.

3.3.3　In traverse network，the length of traverse between adjacent stations on the junctions of different traverses or between a junction station and an adjacent control point of a higher accuracy shall not be more than 0.7 times the length specified in Table 3.3.1 for the specific accuracy.

Ⅱ　Design，Arrangement，and Monumentation of Traverse Network

3.3.4　The arrangement of traverse network shall comply with the following requirements:

1　The traverse network used for primary control of survey area shall be arranged in a loop，and should be correlated with two known directions.

2　Densification network may be arranged as either a single connecting traverse or an interlaced traverse network with junctions.

3　The traverses should be arranged as open traverses，with the length ratio of any two adjacent legs not exceeding 1:3.

4　The control points on different traverses in traverse network should not be excessively close to each other.

3.3.5　The traverse stations shall be located in accordance with the following requirements:

1　Traverse stations shall be located at open places where the substructure is rigid，stable and reliable，and survey stations can be easily maintained，densified，added and spotted.

2　Adjacent survey stations shall be well intervisible.For traverses of third and fourth orders，the line of sight between adjacent stations should be clear of obstacles for at least 1.5m on either side.Those below the fourth order should be arranged to facilitate observation and avoid the effect of lateral refraction.

3　Where electromagnetic distance measurement（hereafter referred to as EDM）is employed，the line of sight between adjacent stations shall be clear of exothermal bodies such as stacks，cooling towers and cooling ponds，and intense electromagnetic fields.

4　The inclination angle of the line of sight between adjacent stations should not be excessive.

5　Use of the existing control points is encouraged.

3.3.6　Monumentation of traverse stations shall be in accordance with Appendix B，and description of traverse stations shall be in accordance with Appendix C.

Ⅲ　Observation of Horizontal Angles

3.3.7　The total stations，electronic theodolites，and optical theodolites used for observation of horizontal angles shall comply with the following requirements:

1　The series categories and basic technical parameters of theodolite shall be as specified in Appendix E.

2　The discrepancy between readings observed with the level bubble at various positions in a level tube or the long bubble at various positions in an electronic spirit level shall not exceed two bars for DJ1 instruments，not exceed one bar for DJ2 instruments，and not exceed one and a half bars for DJ6 instruments.

3　For optical theodolites，the run error and lost motion error of micrometer shall not exceed 1"for DJ1 theodolites，and not exceed 2"for DJ2 theodolites.

4　The deviation of horizontal axis from the perpendicular direction of vertical axis shall not exceed 10"for DJ1 instruments，not exceed 15"for DJ2 instruments，and not exceed 20"for DJ6 instruments.

5　The compensators shall be able to compensate observation values effectively within their compensation ranges.

6　The operation of vertical slow-motion screw shall not result in deviation of collimation axis from the horizontal direction.

7　The displacement of instrument base due to rotation of alidade shall not exceed 0.3"for DJ1 instruments，not exceed 1"for DJ2 instruments，and not exceed 1.5"for DJ6 instruments.

8　The coincidence between the collimation axis（or rays）of optical（or laser）aligners and the vertical axis shall not exceed 1mm.

3.3.8　Horizontal angles should be observed using direction observation method in accordance with the following requirements:

1　The technical requirements for direction observation method shall not exceed the limits specified in Table 3.3.8.

2　Where there are not more than three observation directions at the same station，the observation may not be closed with the starting direction.

3　Where there are more than six observation directions at the same station，these directions may be observed in groups.Such groups shall have two common directions，one of which shall be the starting direction.The difference between angles observed along a same direction in any two groups shall not be greater than twice the RMSE in angle observation of the same accuracy level.The final results of observation groups shall be subject to station adjustment by groups with the same weight.

4　The circle shall be set between observation sets as specified in Appendix F.

5　The average of the observations of horizontal angle obtained in various sets shall be taken as the survey station result.

3.3.9　Where each station on traverse of third or fourth order has only two directions，the left angles of the traverse in forward direction shall be observed with the circle set in the position designated for odd observation sets，and the right angles shall be observed with the circle set in the position for even sets.The total number of observation sets shall be distributed equally to left angles and right angles.However，when observing right angles，the circle shall be reset based on the direction of the starting left angle，or may be reset to the sum of circle reading at the starting direction and the probable value of left angle in the forward direction.The sum of the average left angle and average right angle shall not differ from 360° by more than twice the angular RMSE as specified in Table 3.3.1 for traverses of the specific accuracy.

3.3.10　The observation activities performed at survey stations shall comply with the following requirements:

1　The centering errors of instruments or reflectors shall not exceed 2mm.

2　During observation，the center of bubble shall not deviate from the setting center by over one bar.For fourth order and above，where the vertical angle of observation direction exceeds±3°，the position of bubble should be reset between observation sets，and the observation tolerances shall comply with subclause 1 of 3.3.8.

3　When the compensator fails to function properly or is overloaded due to external factors such as vibrations，the observation activities shall be ceased.

3.3.11　When the observation errors in horizontal angle exceed the limits specified in Table 3.3.8，the direction in question shall be reobserved with the circle set in the same position in accordance with the following requirements:

1　If discrepancy between twice collimation errors in an observation set or the discrepancy between observations of the same direction in various sets exceed the limits，the directions in question shall be reobserved with respect to the starting direction.

2　If the misclosure of round in the second half of observation set or the discrepancy between twice collimation errors of the starting direction exceed their limits，such observation set shall be reobserved.

3　Where more than 1/3 of the bearings in a observation set require repeated observation，this observation set shall be observed thoroughly.Where more than 1/3 of observation sets require repeated observation，repeated observation shall be performed for this station.

3.3.12　When observing the legs with known azimuths that primary control network is connected with，the horizontal observation accuracy for primary network shall apply.

3.3.13　The field notebook shall be checked everyday whenever observations are completed.Where electronic version records are used，the original observation data shall be maintained，and the relevant data and preset tolerances shall be printed out as required.

Ⅳ　Distance Measurement

3.3.14　The leg lengths of control networks of various accuracies shall be measured with moderate/shortdistance total station or EDM instruments.

3.3.15　Short-distance instruments shall be used for measuring distances less than 3km，and moderatedistance instruments shall be used for measuring distance ranging from 3km to 15km.

3.3.16　The distance RMSE of instrument shall be estimated as follows:

Where:

mD——distance RMSE（mm）；

a——fixed error of instrument（mm）；

b——scale error coefficient of instrument（mm/km）；

D——measured distance（km）.

3.3.17　The main technical requirements for leg length measurement of control networks of various accuracies shall be as specified in Table 3.3.17.

3.3.18　The distance measurement activities shall comply with the following requirements:

1　The centering errors of stations and reflectors shall not exceed 2mm.

2　Where any observation data has errors beyond limits，the entire observation set shall be resurveyed.If the observation data distribute in groups，they shall be analyzed for causes and reobserved by taking some appropriate measures.

3　During measurement of leg lengths of control networks of fourth order and above，the meteorological data at both ends of each leg whenever observation starts and ends shall be surveyed.Mean meteorological data shall be used for computation.

4　The meteorological measurement shall be as specified in Table 3.3.18.

5　When the leg length is corrected with the elevation difference measured by EDM-trigonometric leveling method，the discrepancy between elevation differences in vertical angle observation and reciprocal observation can be as specified in 4.3.2 and 4.3.3 for fifth order trigonometric leveling.

3.3.19　The field records shall be checked daily whenever observation activities are completed.If the records of electronic version are used，the original observation data shall be maintained，and the relevant data and preset tolerances shall be printed out as required.

Ⅴ　Traverse Survey Data Processing

3.3.20　Horizontal distances shall be computed in accordance with the following requirements:

1　The measured slope distances must be corrected for meteorological conditions and with EDM system correctional constants before being reduced to horizontal distances.

2　Where elevation differences are measured by EDM trigonometric leveling method，correction for atmospheric refraction and earth curvature is required.

3　Horizontal distance can be calculated using the following formula:

Where:

DP——horizontal distance of leg（m）；

S——slope distance corrected for meteorological conditions and with EDM system correctional constants（m）；

h——elevation difference between transmission center of instrument and reflection center of reflector（m）.

3.3.21　The RMSE of observed horizontal angles of traverse network shall be calculated using the following formula:

Where:

mβ——angular RMSE（second）；

fβ——angular misclosure of loop traverse，or azimuth misclosure of connecting traverse（second）；

n——number of survey stations used for calculating fβ；

N——total number of traverse loops or connecting traverses.

3.3.22　The accuracy of observed distance shall be estimated as follows:

1　RMSE of unit weight:

Where:

μ——RMSE of unit weight；

d——discrepancy between leg distances measured in direct and reverse orders，mm；

n——number of measured legs；

P——prior weight of leg，which equals to 1/σD2（σD is the prior RMSE for distance measurement，and can be calculated based on the nominal accuracy of instrument）.

2　RMSE of actually measured distance:

Where:

mDi——RMSE of actually measured distance of the ith leg（mm）；

Pi——prior weight for the measured distance of the ith leg.

3　Where the legs of survey network do not differ greatly in length，the average RMSE of the measured distances of various legs may be calculated using the following formula:

Where:

mD——average RMSE of measured distances of various legs，mm.

3.3.23　The reduction of the measured leg lengths to projection plane shall be conducted in accordance with the following requirements:

1　The length of leg reduced to the mean elevation plane of the survey area shall be calculated using the following formula:

Where:

DH——length of leg reduced to the mean elevation plane of survey area（m）；

DP——the measured horizontal distance of leg（m）；

Hp——mean elevation of survey area（m）；

Hm——mean elevation of either end of leg（m）；

RA——curvature radius of the normal section of reference ellipsoid along the measured leg direction（m）.

2　The length of leg reduced to reference ellipsoids shall be calculated using the following formula:

Where:

D0——length of leg reduced to reference ellipsoid（m）；

hm——elevation difference between geoid and reference ellipsoid in the survey area（m）.

3　The length of leg reduced on Gauss projection plane shall be calculated using the following formula:

Where:

Dg——length of leg reduced on Gauss projection plane（m）；

ym——average of horizontal coordinates at both ends of leg（m）；

Rm——mean curvature radius of the reference ellipsoid at the midpoint of leg（m）；

Δy——increment of horizontal coordinate between both ends of leg（m）.

4　See Appendix G for the basic parameters and calculation of curvature radius for the reference ellipsoids commonly used in China.

3.3.24　For traverse networks of Class I and above，rigorous adjustment calculations are required.

3.3.25　When performing adjustment of traverse networks，firstly the prior RMSE mβ and mD shall be calculated in accordance with 3.3.21 and 3.3.22 or may be otherwise estimated by the empirical formulas derived using mathematical statistics method，and then the weights of angles and leg lengths can be calculated with prior RMSE.

3.3.26　During adjustment，the calculation sketches and the data entered into computer shall be reviewed，and the calculation results shall be checked.The adjustment results shall be printed out，in which the starting data，observed data and some necessary intermediate data shall be included.

3.3.27　The accuracy assessment after adjustment shall involve the RMSE of unit weight，parameters of position error ellipse or relative position error ellipse，and relative RMSE of leg length or position RMSE.

3.3.28　In office calculations，rounding of figures shall be as specified in Table 3.3.28.