RTK-GPS with freerunner: decimeter-level accuracy with Free Software

Timo Juhani Lindfors timo.lindfors at iki.fi
Mon Sep 27 14:46:18 CEST 2010


in Finhack 2010 I gave a presentation on how I

1) modified the freerunner GPS firmware to obtain raw pseudorange and
carrier phase measurements,

2) used two openmoko freerunners ("base" at a known location and
"rover" that is moving around) with external antennas to capture this
data and

3) used rtklib 2.4.0 to calculate RTK position solutions from this raw

Short summary of results:

1) When both receivers were at a static position it took around 1000
seconds from cold start to stabilize. After that the position stayed
inside a window of 6 cm in all directions for another 1000 seconds.

2) When the rover was moving I was able to easily trace the shape of
an aerial photography marker painted to the ground.

For more information see my posts to the foss-gps list starting at


and the slides of the presentation at Finhack:


Finally, if you are still interested, read about rtklib at


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