[gpsd-users] Differe,tial GPS question

[jouke hijlkema]

Hello all,

Thank you for letting me into your mailing list.
I'm an dutch engineer living and working in the south of France. In my spare time I'm developing a GPS controlled lawnmowing robot.
To get a high precision positioning info I, naively maybe, counted on using gpsd on a RPi and 2 adafruit ultimate gps sensors. One fixed and one on the robot.
The fixed sensor would give me a correction for the mobile one. The implementation so far is as follows:

• The fixed GPS stores its measurements and the error (error = measurement - fixed position) in a mysql database indexed by the timestamp (pulse per second)
• The robot does its own measurements and compares them with the data in the database that has the same timestamp
• The robot calculates its position by substracting the error from its measurements

If I let this run for a day (the robot is stationary) and look at the variations I find that both lon and lat move over 6 or 7 meters which is way to much (I was hoping for ~10 cm precisions).
My question is thus; am I to optimistic hoping this simple setup would work or do you think this should work and I should go over my programming (again)

Thanks in advance,

Jouke

-- 
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| Jouke Hijlkema
| Ingénieur de recherche
| Laboratoire de propulsion ONERA
| tel: +33 5 61 56 63 93
| email: address@hidden
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