Verification with Variety at Javad Training Event, May 6-7, 2021.

Shawn Billings

Shawn Billings
5PLS
One of the topics we covered at a recent training event was using Variety to demonstrate a good solution. I have collected many thousands of points and found that a variety of 1.3 is very reliable. I'm always careful to never say that any technique can "never fail" or is "always correct", but we deal in terms of risk and production. For example, "How likely is a particular method or statistic to failure?". It's an important question for pushing RTK into difficult environments, and at our trainings we try to always setup courses for our field exercises that are in bad environments.

Point 3 was one such point. It was only 2 or 3 feet from the face of a large oak tree (probably more than 24" diameter) with several smaller trees around it and a fairly large cedar tree (about 10" in diameter) about 10 feet away. It was an ugly point for RTK. The red arrow in the Google Street view image roughly points to where the point was.

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I located the point twice with the following screen captures:

20210505-16.44.16_3_1.png

20210505-17.32.16_3_2.png

The first observation met my required value for Variety and had an RTPK observation that agreed with RTK.

The second observation did not have agreement between RTK and RTPK, but the Variety was 2.06. I've been very pleased with Variety of 1.3 or higher, so I felt confident in the RTK observation without paying too much attention to the RTPK result. That was a mistake on my part. The RTPK had two observations that were in agreement. At 60 second processing interval, it is possible for RTPK to have two bad fixes that agree. (It is unlikely that two RTPK results will agree and be wrong with 2 minutes of data each, but at 1 minute each it is possible, even if very improbable).

So what is the take away? For me, it is that RTK with Variety and RTPK agreement remains a very good test for verification. Variety is still a very good test for verification, but nothing is guaranteed. Many attendees observed this point the next day when our training event started and Variety and RTPK were excellent at preventing bad fixes from being stored and were quicker than previous verification procedures.

I share this because I want our users to have the best tools available to them for making reliable measurements efficiently in bad environments. Will this cause me to change my routine? Probably not much. RTK with Variety and RTPK did not agree, so I had a warning sign. I will likely continue to use the profile with Variety of 0.75 Plus RTPK agreement for my difficult shots. If I choose to accept a point with RTK/Variety only or with RTPK/RTPK agreement only, and it does not have RTK/Variety plus RTPK agreement, I will likely test that point with a distance to last, two-point offset, to be certain that the fix was good.

One other thing not obvious from the screen captures, because I changed the coordinate system between the first observation and the second, is that the RTPK results of the second observation were in great agreement with the RTK/RTPK results from the first observation (H: 0.104', V: 0.012').
 

Michael Green

New Member
Using Rover only, North Carolina's rtn, will the results of variety of 1.85 be the same as using base and Rover variety of 1.3
 

Adam

Well-Known Member
5PLS
It's tough to say. The NCRTN does not use BDU in most places. If that is the case where you are the variety number isn't as robust. Look for rtk and rtpk agreement and some time between fixes.
 

Matthew D. Sibole

Well-Known Member
5PLS
I agree with Adam. I would also shoot the point again. I have had a RTK shot that agreed with an RTPK position that was 4’ off of truth. I caught it by doing repeated observations.
 

Shawn Billings

Shawn Billings
5PLS
I think RTK RTPK agreement with bad fix becomes much less likely with more than 2 minutes of data, but I could be wrong.
 

Matthew D. Sibole

Well-Known Member
5PLS
Can you share the screen capture?
Shawn, Here is a screen capture of the bad position. Notice I did not have very long on that particular RTK position but had a total of 677 seconds of data for RTPK to work with. I had over 48 groups of fixes on this shot. I have Confidence set at 15, Consistency set at 5. I have auto accept turned on when RTPK agrees with RTK.

Like I said, I would have caught the bad fix since I shoot everything more than once. The second time on this point I did get a good shot. It still took me an additional 10 minutes to get it though.
 

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Matthew D. Sibole

Well-Known Member
5PLS
I want this project

Sending the project to support right now. Receiver #00163.

Point number 300, 301 and 302 are all the same point. I stored 300 just to show the potential customer how to use Pdelta but I knew it was a bad shot.

Point 301 should have been good based on all visible evidence but was bad.

Point 302 had 2 good RTPK positions on it and I stored it. The RTPK position of point 302 matched the customers coordinates within hundredths from their standard LS position shot in days earlier.
 

Alexey Razumovsky

Well-Known Member
Staff member
5PLS
Sending the project to support right now. Receiver #00163.

Point number 300, 301 and 302 are all the same point. I stored 300 just to show the potential customer how to use Pdelta but I knew it was a bad shot.

Point 301 should have been good based on all visible evidence but was bad.

Point 302 had 2 good RTPK positions on it and I stored it. The RTPK position of point 302 matched the customers coordinates within hundredths from their standard LS position shot in days earlier.
Point 300 has Trimble base processed. PP.301, 302 are processed with Triumph3 base.
1622440176051.png


You might download base file from base receiver and RTPK it. The results will look much better.
1622440572715.png
 

Nate The Surveyor

Well-Known Member
Yes point 300 was from the VRS network. The other two were from my own base.
Well, that should mean some other metric or measure is needed, when using a VRS as a base. Maybe even a splash on the screen, before ACCEPT can be pressed, that warns of this condition?
It seems that local base, with full spectrum constellations has more value, in challenging conditions.
Nate
 
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