PPK Base correction: What i could do better?

Hello all,

I’m a geology graduate student and recently I’ve started to use Reach RS to get precise elevation for my study area. As I’m a greenhorn in this aspect I would like to seek opinion and advice from the community here.

Due to absence of any benchmark information (we found benchmark points but don’t have elevation details), we created some base by using corrections from CORS and I also sent that to CRSC PPP to check our results correction using CORS data. Below is a summary of testing that we did (Longitude, Latitude, Ellipsoid Height)

-7 hours survey period. Correction with CORS using static processing: 25.11511442°N, -78.00543843°E ,-30.7768m. I sent this file to CRSS with outcome very close, 25.11511°N, 78.00543°E,-30.032m

-15 hours survey period. Correction with CORS using static processing: 25.11511296°N, -78.00543021°E,-30.7632m. Again i sent this file to CRSS; 25.11511°N, 78.00543°E,-30.165 m
As im using Emlid RS+, single frequency i can’t send the data to OPUS or AUSPOS as those required dual frequency data.

This base point was used by a survey company before, in fact we are choosing this base point because we would like to have reference to work on. However, their ellipsoid height is different by average about 2m. Their reported result is 25.11510699°N,-78.00542774°E, -28.078m. The brief description provided stated that this was result from RTK FIX with NTRIP set up between Rover and Base. They are using RS2. Unfortunately, i dont have any more data than this.

Hence, i’m seeking for opinion which base result is more precise to work on? (2m variation is huge)

Of course, by nature I’m tempted to use our own survey base data as we know what processes went through but couldn’t just simply put aside what reported before. Therefore, i hope to hear more expert and experience opinions here or any suggestions what are others platform i could use to verify data i collected.

Many thanks for your time.


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Hello and welcome ! After reading your message, several comments.

PPP with single band data is most likely to give inaccurate results, as there is no robust way to deal with the ionospheric errors. What are the accuracy estimates given by CSRS ?

PPP and static differential processing can output results in different datums, so you have to be careful with that and be sure to compare results in the same datum. In what datum are the CORS coordinates given ? And in what datum are CSRS results given ?

With the static processing, do you get a FIX status on the baseline ? If yes, then these coordinates can be considered as good, on first approximation.

Actually the difference between these two coordinates set is at a meter level. This is pretty big, and the explanation can come from the points I mentioned above.

Do you work in the same datum ? And have you checked the antenna height set in the computation ?

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Thanks Florian,
Yes it didnt cross my mind to check those detail you have mentioned. I have very carefully checked the antenna height in the computation but for not for the datum.
After the static processing, i get FIX status for both trials.

From the brief report provided by the company, we are using same datum. I have some suspicion that could be the antenna/pole height. But i don’t have any further mean to verify this as due to absence of detail report or raw data.

Hence, I’m thinking if I’m able to put a case that our experiment of post processing measurement is high precision and accuracy that could be strong reasoning for not using the reading by this third party company.

I would check the datum and revert back to the community. Many thanks again Florian for your tips.


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Hi Ting,

It’s quite hard to provide you with more helpful advices than Florian has already given, @Florian, thank you for them!

I can only add that CSRS-PPP absolute accuracy with single-band device doesn’t exceed 30 cm. So, in your case, it’s better to rely on Static processing workflow. You can even see that Static processing results are much closer to each other than CSRS-PPP ones, particularly in elevations.

And indeed, the resulting coordinates strictly depend on the base datum. When you post-process your log with CORS log, outputting coordinates will be in the same datum as CORS station has. Whereas, CSRS-PPP outputs them in ITRF2020 or NAV83(CSRS) datum.

Keep us posted on your results!