Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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)?


share|improve this question
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)

share|improve this answer
lol, same links – George Jul 27 '10 at 13:11

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.