Angular accuracy of robotic total station (pointing & reading)
I just did a test of the angular accuracy of my S6, which is spec’d at 1″ angular accuracy.
Reason: I have a client who is specifying 4 sets of angles in a survey. There are two levels to this survey, a control network of setup points and then a secondary network of monitored points, to be adjusted separately. They want 4 sets for both types of points. We have been doing 4 sets in the control network and 1 set in the monitoring network for 14 years now. I should add that all of the monitored points are observed from a minimum of two different control points. So I proposed 4 sets and 2 sets, but they want 4 sets. In this network distances range from 5 meters to about 150 meters. I am using a Trimble S6 high accuracy total station. We will be doing hundreds of setups to thousands of points.
So I did a test. Turned 16 sets between a backsight (130 meters) and a foresight (140 meters). Here are some stats I computed. All values are in gons, (0.0003g=1 arc second).
stdev of 16 sets (32 angles): 0.000418 (1.35″), but that is contaminated by the D+R split. The difference between the direct average and the reverse average was 0.000416 (1.3″)
If I average each set (1 set=D+R) and then compute the standard deviation (16 angles), I get 0.000253 (0.8″).
The foresight is 140 m away. If I take each set’s residual and compute the distance subtended at 140 meters, all 16 are under 1 mm. The criteria for the adjusted error ellipses is that they must all be less than 9.5 mm, so I maintain that 1 mm is not significant. In any case I cannot win the argument, just wanted to prove to myself the accuracy and I was a bit surprised. I would say that the spec’d 1″ accuracy has been proven, and it is a combination of pointing and reading error. The 4 sets would be more appropriate if I was manually pointing and/or manually reading the circle. Other errors that affect the results like instrument and target centering errors are not improved by multiple sets.
I also have some data sets that I did with a T2 and a T3, I need to dig those out and see what difference there might be. I would expect the reading error (manual reading of circle) and pointing error (me pointing to precise traverse target) would make the standard deviations of these sets a bit higher.
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