Base with NTRIP Coordinates to use for PPK

Reach Module / M+ / M2
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I have a Reach RS2 that I am using as a base for PPK UAS/Drone operations. My current workflow is that set up the RS2 as a Base and connect it NTRIP using the VRS connection. This results in the VRS that is set up always being very near the actual unit (within a few meters). I wait for the RS2 to get fix and then set it up to average that point for a few minutes. I record both the a) position of the unit average the averaging of the fix position and b) the location of the VRS base. After the drone flight I download the Rinex file. Once back in the office I use the Rinex file and the coordinates I got from averaging the fix position to correct the drone geotags. My question is “Am I using the correct coordinate for the base?” Should I be using as the base the VRS coordinate from NTRIP or the average coordinate of my RS2? Or am I just doing it all wrong? Thanks

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I think it depends on the goal of the drone flight. You need to know a little about coordinates systems and the definition of absolute vs relative accuracy and grid vs surface coordinates.

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I know about coordinate systems and my goal is absolute accuracy. The part I am a little unsure of is what is being recorded in the RINEX of the RS2 when it it connected to NTRIP. Only of the possible base coordinates can be the correct one to use when doing the PPK correction: Either I enter a) the Fix based coordinates of the RS2 or b) the coordinates of the VRS that the RS2 is using for correcting it’s own position. The only other option is that the RINEX file somehow contains information from both the RS2 and the VRS and further processing needs to be done before the PPK processing is done. I covered each of these possibilities in the OP.

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So your goal is absolute accuracy to what? The grid or a surface? If there are logs available from the CORS and you are doing PPK then there’s no reason to have a local base.

Sometimes NTRIP will work and sometimes an averaged local base is fine. There are also occasions where a site requires localization and the base coordinate means nothing.

My point was that not all missions are the same nor are the subjects or clients.

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Thank you very much for trying to help me out here. I really do understand that not all missions are the same nor are the subjects or clients.

Of what you said, Is this really true?:

“If there are logs available from the CORS and you are doing PPK then there’s no reason to have a local base.”

If it is true my question really is useless and I guess that is what you are telling me.

My thought was that using logging with the RS2 while connected to the CORS/NTRIP and using a VRS I would be getting a better correction than just processing with the single CORS later, especially in areas with a longer base distance back to the CORS station.

If this can be done the way I am thinking, I just need to know the proper way is to do it. I have the logged RINEX file from the RS2 (while it was connected to NTRIP), I have the logs from the rover on the drone.
Basically what coordinate should I use as the “base” when I do PPK (The VRS coordinates or the position of the RS2)? I’ve been using the position of the RS2.

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For referencing the site to the NSRS (National Spatial Reference System) here in the USA, use the vrs system coordinates. If just wanting local coordinates, use the average position.

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What do you mean by local coordinates? Both sets of coordinates are in the NSRS. One is the CORS/NTRIP corrected coordinate of of the Reach RS2 survey instrument and one is the VRS being used to correct that coordinate. I just want to know which one the Rinex files logged in the Reach RS2 pertain to.

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This is what I was talking about understanding different coordinate systems. There are NSRS coordinates which are what the actual CORS report. There are corrected VRS in which each node of the network has it’s own corrections. Then you have a standalone base and rover by which the base can be corrected via a CORS or corrected via a VRS. The last one that most people don’t understand or even know about are surface coordinates in which a site has been assigned a coordinate system that is based off of an NSRS and has gotten modified or has a completely arbitrary coordinate system.

You still have not explained the scenario for which you are mapping to what purpose the data is going to be used so there is no way to tell which direction would be best. Either,

  1. Your subject and relatable data are truly on an NSRS system with a 1:1 scale factor and no rotation (highly unlikely) in which you should just use the logs from the CORS (if available) or from the RS2 on a known point directly corrected from the CORS,
  2. You are two far away from a CORS for the logs to be relevant or the corrected local point to be reliable in which you defer to a previously established known point from an engineer or surveyor,
  3. #2 is the case and there are no known points available in which you need to average in a point, but need to transform it after the fact,
  4. #3 is true, but the absolute global accuracy is less relevant than the repeatable relative accuracy in which the base point does not have to be corrected in, but does have to be repeated for each time the site is visited,
  5. The end goal for the data is to integrate with design files which almost surely do not match #1 in which you would need to localize and the base coordinate is irrelevant.
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10

Hi George,

Your workflow should provide you with the absolute-accurate coordinates fine.

If you want to use logs from Reach RS2 base in PPK, you may follow the steps:

  • Average Reach RS2 position using VRS corrections to obtain coordinates with absolute accuracy

  • Record logs on Reach RS2

  • Post-process data in RTKLib using Reach RS2’s position

1 Like
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Awesome thank you for your direct and clear answer.

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