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End-user GPS receivers typically show an absolute confidence indication, such as Within 25 Metres, for the calculated position.

I am parsing NMEA data from a GPS unit and wan't to calculate a similar quality of service indication. The NMEA data exposes a Dilution of Precision indication (actually, one for both the horizontal and vertical position, HDOP/VDOP).

How do I go from DOP value(s) to a concrete confidence measurement (say, metres)?

Thanks.

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up vote 4 down vote accepted

All the GPS receiver is doing, is multiplying the dilution of precision figure by the resolution of the device.

Of course, GPS positions can still be awry, with a high confidence of the location, if you have a good signal strength from satellites in a non-optimum configuration (sometimes referred as canyon effect)

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lol, same links –  George Jul 27 '10 at 13:11
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