Using Post Processed Data

I am working on a project that requires me to locate my RS2 Base unit accurately in numerous locations without the benefit if any known control points. Thanks to help from the forum I have successfully Post Processed my first project. This has led to more questions as I have learned more. In working on setting the base I have reviewed the Tutorial and these two bullet points bring up further questions.

  • (Optional) For absolute positioning: RINEX observations log from a reference station in range of 100 km (60 miles) for RS2 and 30 km (18 miles) for RS+
  • (Optional) For processing improvement: precise ephemeris and clock files from the IGS

How and where does one obtain the logs for the first bullet point. Once one has these logs are they used in place of the Rover logs in the PP process?
As for the second bullet point same question about where does one obtain these clock files?

My next question has to do with using the PP output with results from a Survey. I have PP’d the data from a Survey project and have the corrected path of the Rover as well as the Base location. Is the initial uncorrected base location available somewhere within the logs? Since I need to move my Survey points to correlate to the corrected Base location I need to know the initial Base location to make the adjustments in CAD. Alternatively, is there another way to correct the survey point locations somehow through the PP process or another process? I did take a screen shot before I started my process so I do have the base location for this project but I have older projects that I didn’t record the base points and I was wanting to try to correct their location by the PP method.

As always thanks in advance for your help.

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From a few different options:

  • Local paid RTK-networks, that also provide post processing Rinex files
  • State owned, state-covering geo-reference networks, that also provides Rinex files from their reference bases.
  • Continent-wide georeference services providing Rinex files (like EUREF)

So it very much depends where you are located?

I will also say that while it is certainly possible to post process with 100+ km baselines (and get a fix), I wouldn’t recommend more than 40-50 km if you need centimeter precision (remember the PPM values of the RS2)

What file formats are the files you mention?

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I’m located in the USA, state of Georgia and I haven’t found free statewide sites. I’m sure that there are paid but I don’t have a subscription to trimble or topcon.

Not sure which files your asking about, but the Log files are in UBX and then when converted I have the 3 files of output, NAV, OBS and SBS. My survey files were exported as CSV and SHP.

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I see that NOAA CORS Network - National Geodetic Survey has some stations in Georgia.

Do you have the ubx from both base and rover?

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Yes, ubx from both.

Unfortunately I’m a little far from the few that they have. I’m going to look at the one in Newnan, it is closest.

Do you have a known coordinate + antenna height of the base? Then you can use that against your rover raw-files and get some very nice results.

No I don’t have a known coordinate for the base. My workflow is to go out and survey my points and if there are control points I pick them up and then move everything in CAD to align with the control point. If no control point I try to pick something I can see from Google earth like a manhole cover and then move the points to align with that. I don’t know how accurate google earth images are but it gets me closer than just going off the base.

Roger, if you can’t find a base that is close enough, I suggest using a Precise Point Positioning service like NRCAN’s:

Log for 4-8 (or more) hours, and you get a very decent result back!


Once I know my correct base location I’m assuming I just enter that into my base unit and my survey results will be accurate. At that point it doesn’t seem that there is any advantage to post processing. Is that correct?

Depending on your accuracy requirements and/or environment, the approach you mention should quite fine.

You gain some flexibility and precision from post-processing, but for normal use in good conditions, you are fine.

So how do I make use of the post processing with my survey points? I don’t understand how to take advantage of the data and relate it to the survey.

Hi Frank,

If you don’t have known points nearby, you can get absolute base position using base corrections from a local NTRIP service in RTK or PPK. If you process the data in PPK, you will need to upload the NTRIP base raw data log to the Base Station field, and the Reach RS2 base raw data log to the Rover field.

As an alternative, you can collect the base raw data log for at least 4 hours and upload it to a PPP service such as NRCAN. Please note that you will need to wait for several days to get more precise results, as PPP services take time to get precise ephemeris.

Once you enter the accurate base position in the Base mode tab, you can collect centimeter-accurate rover’s coordinates in RTK without adding any shifts after the survey.

As for the second bullet point same question about where does one obtain these clock files?

It should be possible to get precise orbits and clock files from IGS.

Alternatively, is there another way to correct the survey point locations somehow through the PP process or another process?

To correct the rover’s coordinates after a survey, you will need to calculate the difference between the averaged and precise base coordinates. If you don’t know the base position used during the survey, it’s hardly possible to do it.

I have now done this for a couple of files and it seems to work well. It is a little off from Google Earth’s placement. Makes me wonder just how close you can get on Google Earth.

Thanks for the help.

Don’t count on Google Maps in this regard.

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Thank you for the reply. I had made some incorrect assumptions about post processing due to my inexperience and the amount of new info to digest all at once. I had though that PP using the logs from the Base and Rover somehow magically determined the correct location of the base. After rereading and watching the videos I now understand that an outside data source is needed to accurately locate the Base unit. If I understand correctly that outside source is either NTRIP or sending the Base logs to NRCAN or some similar service. I have tried the NRCAN service for a few files and the process is simple enough and the response time is short. There are questions that I have about some of the settings but I will not get into that here.

I had a lot of difficulty today after entering the coordinates from NRCAN into my base unit. I could not get a Fix. I finally had to go back to Average Single and let it accumulate to get a Fix. Is the Base unit in the Base Mode section the correct place to enter this information? I see that you can also enter Base location in the Rover. I ended up putting the information in both units to try to get a Fix. I also noticed on the Status page that the Base coordinates were not the same as what I had entered and I do not understand why that would be since it was set to Manual. I was using Reachview v2.25.1 because I did not find a place in the setting tab on Reach 3 that shows the graph of the satellites.

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OK, thanks. I am now wanting to understand why my elevation numbers are about 90 feet off from what the survey numbers are on another project. This should probably be a topic for another thread and I need to search the forum and see what has already been posted.

You can also look here:

Good info on stations, data availability and quality of data. Many times people fuss about OPUS not processing their data, usually it’s because the selected stations for PP are down and have no data, which you can see for the station.

Another tidbit of info, you can see the actual crustal plate movement drift/year for each station. Look at the west coast of CONUS stations, it’s amazing.


So if I want to use logs from CORS they are in RINEX 2.11. Since I’ve saved my logs in RINEX 3.xx I’m curious to know if they can be used or if I have to decide before I go out into the field which service I’m going to use and set logging up accordingly.

Most probably ellipsoidal VS orthometric heights.


Frank, I don’t think it matters for the rinex versions. The latest and different rinex versions just have improvements in formatting and additional sats. However if you make your rinex file with GPS only and another file with all GNSS, the only thing the end user will notice is file size. Obviously, using all the GNSS constellations will improve your accuracy.
Just a note and most people know this, OPUS only uses US GPS. If submitting to OPUS, it’s best to create the rinex file with GPS only. You can submit to OPUS with all constellations, but if there are any other GNSS sats at the beginning of the file , OPUS will not process. Also, OPUS will decimate the file submitted to 30 sec intervals.

Here’s some good info on the format of rinex