Hello,

I am subscribed to the State of Arizona's RTN network. I've inventoried the 55 mountpoints and found varying results. When the reception is good I get reliable information confirmed by existing record data. I've been told that it is not recommended for topo work, the vertical is subject to a shift or
phase which I am researching.

Could someone please explain this shift or share their experiences with RTNs?

Your help would be appreciated.

Thank You,

Paul

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Hi Paul

During tests of our independent RTK measurement controller software for Android we've faced the same problem. Different RTN networks and height readings can differ about a few cm. There was a moments where height was OK, but sometimes there has been observed shift. Also the same thing was noticed by a surveyors which work on their software (like SurvCe) in other part of our country (Poland).

kind regards

Mark

Thank you Mark, I've found different degrees of accuracy and would like to find a systematic approach for an adjustment. I believe there has to be a controlled fix... In any event I will keep you posted. Thanks Again, Paul 

First I assume RTN is “Real Time Network” which is a network of CORS (Continuous Operating Reference Stations) consisting of both public & private partners. These 55 “mountpoints” all should have a data sheet that states how they were set so you can ascertain there precision & accuracy. RTN or VPN is only as good as its least common denominator which is cell service. I’ve had good results using Leica’s “SmartNet” checking into points I’ve ran static on in the past with mixed results on other monuments. The vertical component will all ways be the first to be denigrated so I don’t really get “the phase or shift” you’re stating … could you please elaborate.

We made some tests earlier but had very small amount of time for that kind of activity. First time we faced the problem when talking to surveyors that have different equipment - they noticed that different RTK hardware can report heights differently (flat coordinates was OK) - hardware based on Trimble BD970 and Spectra Precision Epoch. But after more tests also using other RTN networks gave the difference so there was something going on.

There was opinions that it can be caused by:
- base station too far or VRS position calulcation errors
- different setup of network base antenna height (especially problems with setup of L1 value in RTN software) [for our side antenna height was setup correctly]
- difference in receiver software that calculate fixed position

To find the source of the differences one have to do more detailed tests on a few equipment which take some time.
Unfortunatelly we had to break the tests, due lot of other work and necessity to return loaned RTK hardware to reseller. In the current moment we want to add support of new RTK hardware and maybe it is good time to back to the tests and look back to this case.

I'm not sure I understand your situation. If you have 55 mount points, I doubt you are getting a network solution (implied by RTN). More likely you are getting corrections from one CORS within a network. If that is correct, getting different results is not very surprising. Every CORS occupies its own location with the unique environmental conditions of that place resulting in differences unique to that CORS.

Networking software by using the whole network simultaneously uses data from all the stations to determine and mitigate the idiosyncrasies. Mount points then are usually many fewer, identified by preferred formats rather than individual stations.

I'm still not sure I completely understood your request, but I hope this helps some.

JAC

Sorry to all...let me clarify....I have 55 mount points or continuous operating stations sending out corrections that I can choose from within the network. I connect to one mountpoint at a time, yes each mountpoint has a data sheet...I inventoried each mountpoint and found varying degrees of reception from my current location....I understand that the longer the base line isn't always an indication of poor reception, there are other factors...Thank you for explaining the differences J.Anthony, it does help.

My question is rooted in GPS legacy which is why I'm asking. At one time it was understood that collected data shifted globally along a vertical angle or plane...if I had a better handle on it I would be able to explain it better, I apologize....Thank You, Paul

After about 4-5 hours of data collection, the geometry of the baseline becomes irrelevant. If performing single base- baselines, after about the same time the length of the baseline becomes almost irrelevant (not counting the ppm of course). 

Most single baseline processing will give ppm of about 1:1,000,000. Most network based processing will give ppm of about 1:10,000,000. This is primarily because the network can mitigate local errors of any of the individual stations.

If actually doing RTN (RTK) then measurements should be repeated about an hour or more later for redundancy and conformation of reasult.

JAC

"then measurements should be repeated about an hour or more later for redundancy and conformation of reasult."

I agree and have always practiced this...Thank you for taking the time to explain, I appreciate your insight.

Paul

You are correct in that this is not a network solutions (RTN) It is a collection of single base solutions.

Tom

Hello Tom, thanks...do you use the AZHMP? If so what have you found? Do you use AZGPS?

Thanks, Paul

Hi Paul,

I've not used either service in Gila County as the areas we are working in typically have cell phone coverage challenges. Our typical critical point recovery seems to like being buried against the slope of a hill that shades cell reception.

I'm the AZGB CORS site owner/operator as well as the AZSV site host.

As a side note the bulk of the state run (ADOT is current curator moving from State Lands) AZHMP single station sites cross feed into the commercial AZGPS full RTN network.

A company I worked with about two years ago rented a Trimple GPS unit to aid us in a "rush" project in Rahway, NJ. Two Leica units were also being used on the same project. To make a long story short the Trimble units RTK elevations varied consistently by 0.15' to 0.20' when compared to the Leica numbers and NGS published monumentation. The Leica used the New Jersey-Delaware SmartNET and Leica DC software and the Trimble used a Trimble networks do Trimble DC software. We did not investigate it too much further and applied a correction factor after we proved the difference between the two. Naturally the field crew took the initial blame, but I'm pretty sure they were not the problem.

I don't know if this is the same shift you are experiencing and I'm not sure why we encountered it, but it was real. We also had a smaller difference in the horizontal and it too was consistent.

Good luck.
Bill

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