When using Weighted Constraints for the purpose of the propagation of error in a TBC Network Adjustment as per the below image, are these values at 1-Sigma irrespective of the projects Confidence Level Display?
It looks like you have performed a thorough analysis of the network adjustment for this particular example. In response to your original question, the weighted constraints for horizontal and vertical are scaled at a 1 sigma regardless of the confidence level.
Subsequent to the above:
As a test, I’ve grabbed a Network RTK TBC Project, and scaled the “Control Point Constraints” as per the project settings at the time when the Network Adjustment was done for 1 Sigma and 95%. Then lastly, entered 1 Sigma Constraints in a 95% Project (all Reports in PDFs attached).
A comparison of the 95% to 1 Sigma Error Ellipse Components shows an average scale up of 3.1, when it should be around 2.448.
A likewise comparison of Height Errors shows and average scale up of 2.5, when it should be 1.96 (via section 3 of SP1 Guideline http://www.icsm.gov.au/publications/sp1/Guideline-for-Adjustment-and-Evaluation-of-Survey-Control_v2.1.pdf ).
However, if you treat the constraints like 1 Sigma in a 95% Project and compare back to the 1 Sigma Project we get the following:
Error Ellipse Components shows an average scale up of 2.48, much closer to SP1.
Height Errors shows an average scale up of 1.98, also much closer to SP1.
In Theory of Errors in Measurements these 3 levels of confidence are defined as:
1 sigma or 1 standard deviation is 68.3% level of confidence used for carthography works
2 sigmas or 2 standard deviations is 95% level of confidence used for surveying and low end geodetic
3 sigmas or 3 standard deviations is 99.7% level of confidence used for geodetic
Maybe TBC should follow these 3 standard deviation or sigmas in its point quality categories by adding one more (unknow, mapping (68.3% = one sigma), Surveying (95% = 2 sigmas) and Geodetic (99.7% = 3 sigmas) as well as used for tolerances horizontal and vertical as well as using in all TBC computations including network adjustment and error ellipse scaling 68–95–99.7 rule - Wikipedia, the free encyclopedia
Thanks Riley so this 1 sigma only is a bug in TBC?
Do you know if this has been corrected Alexander ?
Hi Jesse nope version 4.10 still has this 1 sigma error display and computations bug for the control point residuals used for the network adjustment even if the user has selected in Project Settings 2 or 3 sigmas for the project..... for some unknown reason these 1 sigma errors and residuals in all Trimble surveying software are not being recognized as such nor are they being fixed... Fixing these bugs integrally across all the workflows, computation, adjustments and deliverables should be a priority for Trimble in order to be complaint with applicable ISO standards and be coherent and correct.
Wow, this is extremely concerning!
What does selecting 95% confidence even accomplish in TBC if all the values
remain at 1 sigma?
Joe Blecha, can we please get an explanation on this? Any plans to correct
this? I understand that there is work underway to include the ALTA/NSPS
relative positional accuracy in TBC. Maybe it's time to evaluate and
correct all of this together?
In the meantime, if I want to report 2 Sigma, I must multiply the values in
the N error, E error and Elev error by 1.96, correct?
On Tue, May 22, 2018, 11:27 PM email@example.com <
Jesse the TBC network adjustment is based on least square method so it is no lineal so multiplying by 1.96 the 1 sigma errors doesnt work Also the problem starts in ACCESS 1 sigma residuals display and gets more over optimistic display in TBC results I dont get it why Trimble can not fix it to have the same 3 confidence levels (1, 2 or 3 sigmas) across the whole software line to be coherent?
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