Post-Processing vs Survey Mode with unknown base position

Hi, I am gearing up for field research and trying to solve last minute calibration issues with my RS2 base-rover setup for collecting GCPs

Seeing as my base location is unknown and I dont have NTRIP, I have been using Averaged Single Position for my base mode, collecting the raw logs for both my base and rover, submitting the base .obs to PPP NRCan for processing and then using the results within RTKPOST as my Base Position to get an accurate point for each GCP.

However, I am still confused as to what the difference between collecting the raw logs and post-processing it afterwords or using survey mode within ReachView? It seems that since I dont know the base position from PPP during the actual survey, I cant manually input the PPP results as the base location and correct the rover position in real time. This leads me to a few questions…

  1. If you are recording raw logs for both base and rover, does the rover position get corrected via LoRa within the raw file itself, or only on the points you collect within Survey mode?

  2. Is it possible to post-process all the survey points simultaneously using the PPP results after I submit the raw base .obs? Or do I have to post-process the raw rover files individually if I want to correct the position using the base PPP?

Any insight is appreciated!


Hi, @mhnewton !

In Emlid’s workflow, raw data is independent of the real-time survey on the Survey tab.

In other words, what you collect in Logging is one thing, the points on the Survey tab are another.

Post-processing is still done one at a time in RTKLIB.


You can use Stop & Go method in Emlid Studio app. With it, you gather a single Kinematic Logging raw data for the entire survey and the CSV exported from the Survey tab will organize the name of the points that were collected and how much time was collected about the location.

In this way, the raw data collected in Logging “talks” with the Survey information.


If you correct the base position from CORS then you just have to apply the shift of the base position to the collected points. I am using excel for this.
The only problem is that you must be sure of the projection you use.


Just thought I’d mention that the simple shifting using the correction delta’s for the translation is fine for small areas. However, for larger areas professional translation software is needed as scale factors, earth curvature, geoid undulation and deflection of the vertical components are important in determining the true position of the measured stations. In county wide projects, the error component in horizontal/vertical may exceed 2-3 cm or more without taking this into consideration.


What would your definitions of project size look like? Is 500 acres “smaller” or maybe 1000?

Also do you have recommended translation software? I fear that a Google search will turn up Google translate type sites.

Most professional post processing software does this and can be expensive. RTKLIB is only a single baseline processor. We have JAVAD Justin 3 and also TBC, however I hardly use TBC as we have all Javad gear here. I would recommend Javad’s software over any. It has a fairly steep learning curve and is about $2500 but it’s also considered as a scientific GNSS post processing software used in research. Honestly, it’s in the class of Bernese GNSS Software but is about a tenth of the cost.

There are others out there like CHCNAV and I have a copy of it also, but I haven’t really used it much.
Javad Justin 3 software really impresses me in the ability to filter out bad data. As with anything else, you get what you pay for.

Hi @mhnewton,

Yes, you’re right. To get absolute accuracy of GCPs, you need to place the base over a known point. When you place the base over an unknown point, you will also have centimeter-accurate coordinates, but only in relation to the base. You can read more about absolute and relative accuracy in this article from our docs.

However, you can correct the values of your GCPs in PPK once you get the corrected base position.

After you get the precise base position from the PPP service, there are two options:

  • You can calculate the shift from the base coordinates you averaged in Base mode and add this value to all your GCPs coordinates

  • We’ve recently released a free beta version of Emlid Studio - our desktop application for PPK. It has a Stop&Go feature. You can post-process raw data logs from base and rover using the corrected base position. To learn more, you can check our docs

Raw data files contain observations from satellites that can’t be corrected. So, corrections from the base in RTK are applied to points in Survey mode only.


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