DPOS vs Long Range RTK (15.9mi)

[Shawn Billings]

Yesterday I was talking to John Evers about what I had been doing for the day. I had one Triumph-2 on our office base station broadcasting RTCM 3 corrections over TCP. The job site was 15.9 miles from the base. I carried a second Triumph-2 to be used on site as my base with UHF.

I collected a point, L001, with the rover using the office corrections, 15.9 miles away. I collected for 1500 epochs at 5Hz. I then set the second Triumph-2 as a base on this point and collected points on site. The on site Triumph-2 was collecting raw data (as is mandatory using base rover setup). I submitted the raw file from the on site base to DPOS this morning.

John asked me what I expected the variation to be between the DPOS position and the 15.9 mile RTK vector. I guessed that it would be within 0.10 usft horizontal and 0.2-0.3 usft vertical. The results:

Horizontal shift: 0.07usft
Vertical shift: -0.20usft

Pretty amazing results!

I would not recommend doing production work at this range. Collecting the 1500 epochs required quite a few minutes because fixes are not as fast at this range. I think it's fine for establishing an on site base point as I did here, but I wouldn't want to collect numerous points this way.

15.9 Mile Vector:


DPOS Solution:

 

[Nate The Surveyor]

What's the maximum range for genuine productivity, from an rtn? I have another surveyor down here, who wants me to go in with him on an rtn station.
I declined... Dpos, and my own base, at 5hz seem indispensable.
Others seem to use rtn's, but I wonder how big of an error ellipse this generates....

 

[Adam]

Nate, It depends on VRS or using one cor's site. I use my states RTN which creates an imaginary base near me. You can use it anywhere you have cell service and cors. I bring in SPC via the network then set up the TRIUMPH 2 to take advantage of 5 hz.

 

[Nate The Surveyor]

"creates an imaginary base near me."

Does this mean, you select a geographic location, near you, and it interpolates the difference between the COORS stations, and applies the weather corrections, and temperature, and pressure corrections, and the geoid corrections, to generate this "Imaginary Base"?

 

[Adam]

"creates an imaginary base near me."

Does this mean, you select a geographic location, near you, and it interpolates the difference between the COORS stations, and applies the weather corrections, and temperature, and pressure corrections, and the geoid corrections, to generate this "Imaginary Base"?

Your location is sent to the network provider via the internet, base coordinates get calculated but the these base coordinates can change automatically too. Say for instance you hop in the truck and drive a few miles. So the VRS base is always close to you. You can also use 1 cors station if you want, you just have to select the base mount point.

 

[Shawn Billings]

I wouldn't use long range RTK for production. Like Adam, I would use it for establishing a coordinate on site, then use my own base on site. I would then probably use DPOS to refine the position of the base even though I have a position from my office base station.

I also use Long Range RTK for recon. I can navigate to known coordinates with great accuracy with minimal effort, within seconds of arriving on site.

I use my office base for anything within six miles of the office. Beyond that, I think I see better performance with an on site base station.

I'm not using a VRS, just single base. Because my office base is a Triumph-2, I still get to use Beast Mode pushing corrections at 5Hz. It actually works better over IP than UHF in my opinion.

In previous testing of the Triumph LS at various ranges, I have found precision to be:
He(RMS) = 5mm + 0.7ppm x BL and Ve(RMS) = 10mm+0.7ppm x BL

This is not Javad's specification, this is my own observation using 240 second observations at 1 Hz. I determined this before Beast Mode was released. A 15.9 mile (25.6km) vector would have a potential horizontal error at 1 sigma of 0.075' (0.023m), a vertical potential error of 0.09' (0.028m). For the 2 sigma error you would multiply the 2D by 1.6 and the vertical by 2, so that would be 0.12' and 0.18'. Again, this is all based on my personal observation and not Javad's published specifications. But it certainly appears to be a pretty good rule of thumb.

 

[Adam]

Very rarely do I get to do a job within 6 miles of homebase.