Friday, 10 August 2012

GPS Tip - Position Averaging

Today's GPS tip is using position averaging.

Most mobile GIS software defaults to using one single GPS
position to define the XY of a point feature. That's quick but it
may not be very accurate.

Say that the accuracy of your GPS unit is 3 meters. You can imagine
an imaginary 'accuracy circle' with a radius of 3 meters extending
out from your GPS position.

When you start logging GPS data, the positions come in at whatever
frequency you've specified - maybe one position a second.

The majority of those positions will fall within the imaginary
accuracy circle - some of them closer to your actual location,
others farther out along the perimeter of the circle.  Some will
even fall outside of the circle entirely.

If only one GPS position is used to define the feature's coordinate,
it may dead-on at the actual XY, but it might just as easily be
outside of the circle - a difference of 3 meters in this example.

Position averaging allows you to collect several GPS positions
instead of just one.  Most will be in the circle, some will not -
but all get averaged together.

That averaged XY becomes the final coordinate of the point feature
and it's a very simple way to improve the accuracy of point data.

Happy Mapping!

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