### WHICH METHOD OR INSTRUMENT ARE MOST ACCURATE USING GPS OR TOTAL STATION?

I'm using trimble R8 gps for subdividing of 500 plot with different area per plot in an open and flat area of around 3 square kilometer, but when i tried to use my total station (Trimble 5600 DR200) with same Benchmarks there are a shifting of around 10 centimeter,area of the plot is same as per coordinates computation methods,only the shifting is the main problem.(find the attachment)..

please to all well experience land surveyor and government surveyor give me some advice.thanks and more power to the LSU.gps%20and%20total%20station.pdfgps%20and%20total%20station%202.pdf

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#### Replies

• In my opinion, the difference is a simple geodesy issue. RTK positioning is a truely geodetic work while total station positioning is a locally based endeavor. For that reason, I would say that there are seven basic transformation factors that caused the difference.

• Julius, it is a basic for several contract that the client provides primary control points that will be initially used for all survey works. Therefore, for such big area, you should do your circuit and close it based on the provided references, with the client or engineer's approval, thus, utilizing the new control points for setting-out.

Your instruments are of good specs, meaning, should have good survey result. The one i mentioned earlier is a basic construction procedure. Anyway, if you want to utilize only a single baseline (Pts. provided by the client), and considering the type of work, better to use RTK, otherwise, using a total station without applying corrections and no adjustment will cause accumulation of errors resulting to erroneous survey.

For me, it should not what instrument is better that was put in question, it is on the survey procedure.

I hope you got my point... Good luck...

• ok sir thank you very much i got your point.

• this is a scale factor problem .. we need to calculate scale factor and we need to enter the value inside the total station

• In my point of view, It should not have such discrepancy. I believe that the survey procedure have a problem. If i will work for that, i should establish a control network first using GPS and do proper adjustment. Afterwards, do setting-out using total station or rtk using adjusted control points.

• Mr Eric i am using benchmark established by government with high precision of x,y and z, R8 base and total station are setting that benchmark but still 10cm discrepancy,and also that 2 instruments are new calibrated,but anyway thanks for the reply,now i will focus using R8 gps with rtk survey maybe gps is more accurate than total station.

• the bench mark that i am using is established by the government with high precision of x,y and z.

setting out using adjusted coordinates are ok but we cannot say which are the good method between gps or total station.but anyway thanks for the reply, i will focus now using rtk survey with R8 gps.

• I think that in both methods you'll get less than 10cm, in your case it seems to be a different set of coordinates in the benchmarks.

If you are using RTK sometimes the correction in the vectors tend to move the rover in the "same direction" over a period of time, you should take some control points to check that.

Also check the 3D distances (point to point) with a total station and watch if they are the same as the GPS.

• Party Chief

I'll pass this along and try to share it with surveyors that I know will have the answer, but in the future, you might consider posting this in the Trimble Groupin order to get targeted feedback from Trimble Users.

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