Introducing the Freerunner Navigation Board

Helge Hafting helge.hafting at
Wed Jul 21 10:55:09 CEST 2010

On 03. mai 2010 11:10, Jeffrey Ratcliffe wrote:
> On 3 May 2010 11:04, Dr. H. Nikolaus Schaller<hns at>  wrote:
>>> Having navigation work inside tunnels
>>> would allow mapping them accurately for openstreetmap. And also have
>>> underground navigation - some tunnels have got
>>> intersections/roundabouts inside, with several possible exits.
> Would navit, tangogps, etc. need a new interface to access the
> sensors, or could the existing libraries be adapted to "correct" the
> GPS data with additional information from the extra sensors before
> handing it on to the GUI?

The natural place for such software seems to be in gpsd itself - it 
already supports having several gps (position) devices. (Or possibly in 
a front-end to gpsd - depends on what the gpsd developer wants.) But too 
many processes / software layers is not good - it causes delays.

navit, tangogps etc. should of course not need reprogramming, you can't 
fix every program out there. Especially not the proprietary ones.

The software should simply pass through gps data as long as it arrives, 
and the precision is sufficient. This data can be used for continous 
calibration of the magnetic/inertial/odometer inputs.

When gps precision drops below intertial precision, or when gps drops
out completely, the software should keep sending position updates based
on inertial data. On your display, the map software will then tell you 
that you have 0 satellites, but still update your location on the map.
Another use: interpolate position between gps updates, so you
can have a 10 FPS map if you like.

As the software auto-calibrates the inertial system, it can know
its precision. So it can report how the gps-less position data 
deteriorate over time, and perhaps stop when precision gets so bad that
the inertial data is no better than assuming you just stopped at the 
point where you lost gps coverage.

An inertial system with only accelerometers will go bad quickly, unless 
you have some really good accelerometers. A system with odometer and 
magnetic compass can keep you going for a long time and do better than 
the simple "stopped due to missing gps signal". In particular, the 
odometer will know when you are standing still - you can only loose
precision when moving.

Helge Hafting

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