Using a GPS base station to get +-3cm accuracy? Any thoughts?

vanmunch

Hello,

I was wondering if anyone has tried connecting a GPS & base station to the Propeller? Or any other ideas to get accuracy of +- 3cm accuracy?

To jump start the conversation I've been doing a little research on "precision agriculture" where they can get +- 1inch 95% of the time year over year using a base station and Real-Time Kinematic (RTK).


http://www.trimble.com/agriculture/aggps-rtk-base.aspx?dtID=overview

http://www.trimble.com/agriculture/gps-for-agriculture.aspx

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My wife is very, very understanding

kf4ixm

I did some research once on this, but for the life of me i can't find the links now. From what i gathered, there are stationary usgs base stations scattered across the us, and these stations transmit a time-base signal. the reciever (designed for rtk measurements) picks up these signals from 2 or more and calculates these time-based signals along with the signals from gps satellites through triangulation. somewhere on the usgs site, there is a page that has these sites listed, along with thier info and location.

Ok, i was wrong, it's on the noaa NGS site, it's called CORS (Continuous Operating Reference Stations). there is a google map on there for the different sites...

http://www.ngs.noaa.gov/CORS/
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max72

This is called DGPS (differential GPS).
You get a RELATIVE accuracy up to a centimeter or two. If the base position is known then you have absolute accuracy too..
The trick is many GPS errors are related to atmospheric effects. If two instruments talking each other are close (theory says up to 20km) the error are the same and if you make a difference you get rid of them.
I have such a system for land survey, and it works smoothly, but uses two frequencies (even part of the L2), precision antennas, and a lot of processing power do find a good solution. Moreover the firmware finding the centimeter accuracy solution is the key point.
Another aspect it the base must send a stream of data to the mobile unit (the rover), so that the rover can do the calculations.
You can use your base, or a third party public/private base.
The correction parameters can be sent in many standard formats. Connection can be based on radio, telephone, machine to machine, or internet.
I don't know if it is possible to do a DGPS with the propeller, but it would be a hell of a job. On the other hand the result would be extremely cool!!