I'm curious about the accuracy of the Free-Stationing function in Leica-1205 Total Station. I made a simple experiment by comparing the results from free stationing with their counterparts that were established from a previous survey and I got differences of up to +/- 6 mm in the three coordinates. To confirm that there is not setting problems, I measure the same coordinates that were computed by the Free-Stationing with a new azimuth and a new starting point for the location of the Total Station, then I used the 3D similarity transformation to compute the transformation parameters between the two sets of the coordinates and we got an accuracy of less than 2 mm. In fact, this finding rise a question on how the Free-Stationing is implemented in different Total Stations. I do appreciate your feedback.
Dear Dr. Gamal,
please find the attached data sheet including accuracy,
http://www.xpertsurveyequipment.com/total-stations/leica-tcrp1205-total-station-tps1200-series.html
best regards
Interesting, I have wondered the same thing.
The increase in errors from your free-stationed instrument location could be due to a higher margin of error in the location of your referenced control points when compared to a simple instrument setup and single backsight. Even if one point has a larger error, that could throw off the final orientation. Also, it might depend on what methods you used to find the "true" coordinates of your control points- especially if were they originally set from a single-backsight instrument orientation (and definitely if set from the same setup and orientation).
I typically would only use free-stationing after a traditional closed traverse loop has already been established and balanced. Even then, I would remain skeptical using that setup for any more than lower accuracy workflows, such as a topography surveys or tree locations. +/-6mm is actually a bit better than what I would expect from a free-station setup. That is not bad.
Granted, I am not familiar with the free stationing in Leica software, or the 3d similarity transformations (similar to least-squares?), but that is the way I see free-stationing in general.
Regards,
WW
Dear William
First of all, thank you very much for your interesting feedback and comments. In fact, my question came while I'm teaching my students an introductory course in Geomatics. This comparison came out of curiosity and after this comparison I became very interested to know about the implemented algorithms for free-stationing or resection in different Total Stations. As is well known, free-stationing is very critical function for stakeout work. I will do more investigation in this issue.
Regards,
Gamal
Yes, it is a handy method when you need it! I have seen people use free stationing for construction stakeout, amd it seems to work. Maybe I should trust it a bit more, or even try my own comparison tests.
Sounds like a good test, good luck!
W
There is no general answer to this question. The accuracy depends not only on the instrument you use, but also on configuration of target points and their accuracy. To get a final answer you should have a network adjustment for your measurements.
I agree with William J Wright.That is depends on user professionalism.
Anyway you should have more measurements than necessary (redundant measurement configuration) to avoid critical errors having an influence to your result.
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