RTK, vs RTPK wide open areas, setting control.

Jim Campi

Active Member
I have not done any studies on this. Only antidotal evidence. I am getting ready to extend some control for a roadway project done back about 15 years ago (only 3 original control points left). I plan on occupying each point 4 times. I plan on taking 3 minute observations each time and rotating the pole 90deg each shot to eliminate pole leveling errors. I will use RTPK observations on each one likely.

I will also likely do some testing with this extension as well. I will run static 2 hour sessions on each point and compare them to the averaged RTPK data.

I would have to respectfully disagree with John in that 5-20 second observations would not give me enough time to average heights that I would feel comfortable with. However, that is my personal opinion. Take it for what you will.
Matt, you mention rotating to eliminate leveling. Is the antenna calibrated properly when aligned north? Is that only when connected to CORS?
 

Jim Campi

Active Member
I would think so. Waiting 20 seconds for a fix on each point is a long time. Is this in the open or with multipath? How far away is your base? Are you using UHF? A network?

If you're doing hundreds of topo shots, you probably don't need to worry about pole leveling errors. Point the rover whichever direction works and keep moving. If you're setting control and trying to eliminate small errors, averaging shots with different pole rotations makes sense.



Probably. If you export kml from the T-LS do the points match the Google Earth image?
How long do you occupy on a point (in open sky) for a topo?

John, I will try exporting to kml and see how it lines up.

One more quick item, if I want to switch to a new page and change the coordinate system (so I have 2 coordinate systems, one on each page, for the same project) is that possible? How?
 

Nate The Surveyor

Well-Known Member
Jim, give John Evers a call. He can help you understand "pages" and coord systems.
The javad LS uses lat Lon for its native coord system.
It has 10 pages. Each page can be assigned a different coord system, which is really just another expression of lat Lon onto some plane.
 

Matthew D. Sibole

Well-Known Member
5PLS
Matt, you mention rotating to eliminate leveling. Is the antenna calibrated properly when aligned north? Is that only when connected to CORS?
This is not just when connected to CORS it is all of the time.

Nate is correct also in the fact that each page can have a separate coordinate system. Our native format is WGS84 as can be seen when exporting a PDF file. The first page of the PDF shows what transformation is being applied. There are no tricks to it. The program knows what transformation needs applied between WGS84 and any state plane system in the US and a multitude of others.
 

Mark Wheeler

Active Member
With the latest software, the State RTN (Leica Spider Network), my RTPK and RTN results vary radially from the the direction to the nearest CORS, with the difference increasing with the distance from the nearest CORS. For example, at my house the nearest CORS is 11 miles due south (+/-). When running off the newtwork RTPK is typically N 0.09, W 0.006. Likewise, if the nearest CORS is N 45 W RTPK 14 miles, RTPK is typically S 0.08, W 0.08 (example). Very consistent, but of concern to integrity. The network is not VRS, but appears to use all the CORS to position the network server and provides the corrected position from the nearest CORS to the rover. The issue seems to be similar to earlier posts in this thread for Radial differences from their JAVAD base setups.
 

Mark Wheeler

Active Member
Alexey, I sent project 22-6-27 TEST to support. Points 1,2,5 & 6 were for 15 minutes. Note: Point 1 did not utilize glonas (low coverage). Let me know if you do not receive it.
Previous value for this point was N 2986375.756, E 611731.584, EL=270.680
 

Alexey Razumovsky

Well-Known Member
JAVAD GNSS
5PLS
To check position radial dependency 2 CORS (MAWM, WES2) were used for post processing
1656223171955.png

Local base is on the bottom. Points 1-6 are in the center of picture.
Below are RTK and RTPK solutions.
1656224540397.png

Purple dots are RTK epoch solution. Orange vectors are RTPK.
RTK is a bit shifted towards North. I beleive the disagrement is in a range of errors. RTK and RTPK use different sets of GNSS signals.
 

Mark Wheeler

Active Member
Hi Alexey,
Enclosed is a quick comparison of RTN (RTK), RTPK and DPOS for points 1,2 5 & 6. I realize you can't always tell a lot from 15 minute observations. With this site the DPOS were generally south of the RTN points and the RTPK were generally north of the RTN points (radially from nearest CORS). I also enclosed another site with that was much closer to this CORS. The difference between RTN and RTPK was significantly smaller, but in the radial direction. I am looking to determine whether the RTPK is more correct or if the RTN is more correct. Again, tough from the limited info, but I know at Site 1 RTPK is always a tenth or so more north than the RTN.
Thanks for looking into this. Much appreciated.
Mark
 

Alexey Razumovsky

Well-Known Member
JAVAD GNSS
5PLS
Hi Mark,
DPOS provides an adjusted solution tied to multiple CORS. RTPK provides a solution tied to local base. So radially impact would be eliminated in DPOS after adjustment.
 

ken larson

Member
I had two sessions of data on the same point. First session deep sixed for some reason and I needed to reboot ls+ and t3 and start again. Both sessions begain with an auto position. After cors processing base data for both sessions the results are 0.265 hor and 0.79 ver dif. The base was not moved. Just rebooted between sessions.

File was uploaded to support as 99-007 2022-06-24A

The 2 base points were 90064 and 90055

Base point 90000 was also not where prior locations would have put it

Thanx in advance for your input
 

Alexey Razumovsky

Well-Known Member
JAVAD GNSS
5PLS
I tied points 90055 and 90064 to 3 CORS manually in Justin.
1656394789810.png

Every set of solutions pointed at separated receiver location (see picture below)
1656394868567.png

Looks like you have moved receiver between sessions.
In the meantime 90055 session is 13 minutes only. So you might neglect a solution for 90055.
 

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ken larson

Member
I tied points 90055 and 90064 to 3 CORS manually in Justin.
View attachment 12913
Every set of solutions pointed at separated receiver location (see picture below)
View attachment 12914
Looks like you have moved receiver between sessions.
In the meantime 90055 session is 13 minutes only. So you might neglect a solution for 90055.
Thanx for looking. The rover went to cdf and would not resolve, so I walked back and the base and rover was powered off and back on and a new auto point was started as 90064 and never moved from tripod. Does this mean a base occupation of less than 15 min will not provide a percise location after DEPOS?
 

ken larson

Member
Thanx for looking. The rover went to cdf and would not resolve, so I walked back and the base and rover was powered off and back on and a new auto point was started as 90064 and never moved from tripod. Does this mean a base occupation of less than 15 min will not provide a percise location after DEPOS?
This has happened at least one other time that I have caught...maybe a month ago. In that instance I had returned to a job site and occupied a known point...started to work and slipped into CDF that would not resolve....rebooted base and rover and continued only to process base data later and have multiple positions for the same point.
 

Shawn Billings - Javad

Active Member
JAVAD GNSS
As Alexey says, minimum observation length will definitely vary depending on the CORS distances. In my area I believe a 15-minute observation is about as short as I can go, but I have a pretty good density of CORS stations. In other places with more distant CORS, I would definitely stay longer.

I'd be interested to know what your DPOS report shows for the residuals of position. I suspect that you will not have low residuals on your 13-minute solution.
 
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