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I recently connected a GPS unit sold by Adafruit to my Raspberry PI and looked at the data feed. The data I'm getting for speed seems to be way off. My PI is stationary, but it always reports are moving at about .5kph. It will occasionally go up to 1.5 kph.

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The Speed Err is reported to be +/- 19 kph! That seems a little odd. Do I just have a bad signal indoors or is this to be expected? Is there any way to correct for these wandering readings?

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this is perfectly normal, especially indoors, where the reception quality is far from ideal. your GPS unit recalculates your position every time, and because of the position error, it thinks you're moving a bit back and forth, hence the non-zero speed readings.

to fix this you may get an external antenna or average your coordinates over time to get more precise location.

  • Averaging wont work because it's always > 0 kph. I'm going to use the GPS to track the speed of a relatively slow moving object (around 15mpg average) so being off by almost 1mph at times will make a big difference. It will always be used out doors so that may help. I guess I'll have to go outside and see if there is less error. – Sparafusile Oct 3 '13 at 13:00
  • @Sparafusile average the position and calculate the speed yourself. – lenik Oct 3 '13 at 23:31

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