Emlid

Setting up base- SBAS (WAAS) or CORS


(Bcarter) #1

Dear Emlid Community,

I am in the process of setting up a new base station. I need it to be as accurate as possible. I plan to use post process with a local CORS station using their RINEX logs. However, I can also “see” SBAS satellites (part of the WAAS system here in the US). My question is, do the SBAS satellites also provide correction data? I am under the impression that was the entire purpose. Does Reach take this into account? If so, how? I have looked through the documentation and through the forum, but, honestly, some of the information is contradictory (which may have to do with different versions of RTKLIB and/or ReachView).

Thanks in advance.
Cheers,
Ben


#2

Well… Yes. But alone, it does not give you the amount of correction i guess you are looking for (~cm?)
You can you use it in addition to the other system but thats about it.

For a regular gps in single mode with and without sbas, you might improve the accuracy to a level it is noticeable.

About sbas and similar system


(Bcarter) #3

Thanks @TB_RTK . It sounds like SBAS (WAAS) will not help with base setup since I do want it to be as accurate as possible. However, I had a hard time figuring out exactly what SBAS was doing. I couldn’t find file format, etc. Does it send RINEX? NTRIP? I checked the WAAS website and couldn’t find this. Admittedly, I am trying to figure out what SBAS is sending and how that can affect the GPS reading. I read somewhere that the SBAS signals can be used like the GPS satellite signals. Is this false?

On a different note, I think I was kind of hoping that SBAS would provide similar corrections as CORS, but live and in-the-field instead of via post processing. Is that was SBAS is doing? Is it not as precise because the data I submit to CORS will be collected over hours?


#4

Sbas is broadcasted along with the other messages, basically ordinary satellite but with added sbas message.
In the link i gave its described was sbas is but its not the same as cors.
Maybe this will help understand it better
https://www.gps.gov/systems/augmentations/


(Bcarter) #5

Thanks again, @TB_RTK

I had found that one and it is great for general concepts, but not on the specifics. I think I found what I wanted in the RTKLIB Manual. This also had a bit more information: http://www.sxbluegps.com/technology/sbas-made-easy/

And, this statement from Trimble may be the most help: SBAS corrections should be used to obtain greater accuracy than autonomous positioning, not as an alternative to RTK positioning.

Of course, that is essentially what you indicated in your first reply. I’m getting there.

A further question… So, if I set up an RTK base (using CORS, etc. as discussed above) that is very accurate, then does the inclusion of SBAS aid at all in an RTK survey? It would seem like the RTK would already be more accurate than the SBAS could provide, so then should I eliminate SBAS in the RTK survey? Or will it provide just one more correction mechanism that may improve the RTK rover locations (if only marginally)?

I also want to stress my appreciation for @TB_RTK and others who are willing to deal with those of us who are much less experienced.


(Timd1971) #6

I second that! There is a handful of people here that “really” know there stuff…which helps us greatly!

bcarter, from what I understand, obviously the more satellites, the better…SBAS is just another to add to what you may already be getting such as GPS, GLONASS and Galileo in the USA region. I think the CORS is what will help you here in getting absolute accuracy from its base starting point for your rover(s) to carry on from. Or maybe you can find public records of some known points in your area to set your base up on and leave someone there to watch over it?


#7

It can. If you think of it as a ordinary satellite and that particularly satellite is perfectly placed in the sky that gives your RS a better satellite geomtry for fix, but not because of the sbas function. This is because and i assume cors has a basestation closer to your rover then the sbas has calculated a augmentation map. So real data from a closer base to your rover will outperform sbas data.

This is like for your rover to hear one system telling it is located at A with 50% chance of beeing right and a another system with better intel telling is located over at B with lets say 90% chance of beeing right, and the rover is smart enough with filters and listens to the system giving it the most likely correct data. The atmospheric data is more right when base is closer to rover then the atmospheric data thats been calculated from a grid of bases further away.

This is how i had imagin sbas works with other systems, so i hope its right


(system) #8

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