How to determine the accurate base-station position using CORS Data?

Q&A forumCategory: QuestionsHow to determine the accurate base-station position using CORS Data?
ghillert asked 4 weeks ago

I believe I have now a fairly decent setup for all my awesome Ardusimple gear using a base-station and a rover. However, I am currently using the survey-in mode for the base station as I don’t have any NTRIP stations here in Hawaii from which I could get correction data from. This provides very good “relative accuracy” but the “absolute accuracy” is just so-so, e.g repeated measurements don’t seem to overlap perfectly. It would be nice to eventually “repeatably” conduct those mythical 2+cm accurate measurements. My understanding is that using CORS data from an official station the position of the base station can be determined very accurately, even if the CORS station is 40km away (in my case).
Are you aware of any good guides for that? I believe I will eventually be able to connect the dots but the information available is a bit limited. Maybe this would be an amazing resource for your blog 🙂

Ardusimple Staff replied 4 weeks ago

Hi ghillert,
Few alternatives:

1. If your CORS station is providing real time RTK corrections, you should be able to connect your base station as a rover to the CORS NTRIP caster. It will take a bit longer but in static conditions at 40km you should be able to calibrate the position of your base station, so then you can use it as reference for your other rovers.

2. If your CORS station only provides post-processing service, send them RAW data from your base station, and they will tell you which is the position of your base station.

3. If you have a CORS network in your area, there’s usually so-called calibration points / geodetic points. If you find can find one within 50km from your base station go there and switch roles. Setup a temporary base on the known point and calibrate your other unit in reference to that point. You will have to setup a real time connection via internet to send the RTCM corrections from one unit to the other.

ghillert replied 4 weeks ago

Thanks for your quick feedback. Things here in the Pacific are a little less “advanced” I suppose 😉 My closest CORS station: I think the only thing they offer is a download of the RINEX data. Which I believe can be post-processed using RTKLib together with a recorded log of my base station data and that should yield a correct base-station position. But that’s where my knowledge starts to get fuzzy.

I believe in my case only option 3) is maybe an alternative.

Cheers, Gunnar

ghillert replied 4 weeks ago

I believe for option 2) in the US you can use OPUS (Online Positioning User Service) at https://www.ngs.noaa.gov/OPUS/. You can also select the calibrated Ardusimple Antenna at https://www.ngs.noaa.gov/ANTCAL/ –> “AS-ANT2BCAL”

Ardusimple Staff replied 4 weeks ago

Correct.