Hi,
I use a Sokkia GSR2700ISX as Network Rover on my country's CORS.
I have noticed that if I work far away from the physical base station (say 10 or 20 km) my vetricals differ by +- 10cm every time I go to the site i work.
For example one day I shoot a nail with RTK and the Z value is 100.25m and the other day the Z value is 100.35m.
The same happens either I work with the Nearest base station or VRS or MAX.
Is this normal, has to do with the RTN? Is the receiver problematic or the settings incorrect?
What is your experience?
P.S. Sorry for my English, it's not my native language.
I have found that time of occupation is critical. I use the same sokkia gsr2700isx, but only for static collection now. I use a leica gs14 on an RTN and have seen that same problem. I believe it's all about how long you occupy a station. That's why I always will tie into several benchmarks when I am using the RTN for topographic work.
Dtp
gto234
I have quite a bit of experience with RTN. Your example is not that uncommon and any equipment will perform the same.
Just set out on a point and observe real time height readout. I'll bet you will see some variation over time. Often you will see a jump when a satellite jumps in or out of the solution. We have taken 24 hours worth of 1 second epoch observations and thrown them in a spreadsheet. The high and low during the 24 hour period is almost always at the 10 cm level. However the average is balls on. The farther you are from the base the wider the spread and no its not a single base line solution its a network solution. Also high humidity is not helpful in my opinion. My opinion is that network modeling isn't as robust as advertised 20km from a base under some unpredictable conditions.
Thanks, these answers covers my question.
I must apply different workflow and take more shots during the day (if it is possible) and then average the coords.
However I noticed that if I am near the base station (eg 1km) the results doesn't vary so much.
For those who work with base-rover at max 5km baselines does this variation of verticals happen?
Short baseline base - rover RTK is definitely more reliable than network RTK, but 2 - 4 cm fluctuation in the vertical is still pretty common, and that's assuming everything is working right and the conditions are good. Multipath, poor radio reception, electrical transmission lines, obstructions, etc. can increase that number quite a bit.
We do multiple independent three minute occupations when setting site control with VRS. The 10cm variance that you describe used to be a lot more common; the latest upgrades to the servers and software seem to have tightened things up a bit, I'm seeing much better repeatability.
If the nearest station to you in a VRS network is experiencing high latency in its data that can create major problems. Pocket thunderstorms that we commonly get in the summer, especially fast moving ones, can also create problems with the ionospheric modeling in a VRS. If the nearest station to you is in a thunderstorm and you're in sunshine you're probably going to get inconsistent results.
