[Openstreetmap-dev] DOP and errors in meter

Erik Johansson erjohan at gmail.com
Mon Dec 26 17:52:37 GMT 2005


Hi,

The code that stores the track logs will store a DOP value, which
means "Dilution of Precision" it's something that the GPS give you as
an error estimation. Some GPS devices will also spit out a more useful
error estimation in meters. I've never really 100% understood how DOP
correlates to errors in meter, but....

I made some track logs during Christmas eve, and discovered that I had
upgraded GPSD to a version that no longer includes the DOP value from
the GPS. This means that I have a value that is in meters instead of
the DOP thingy, GPSD will automatically convert it according to some
formula. How should this be handled?

1. convert all dop values to meters
2. store both dop values from GPS and err. estimate in meters.
3. just use dop nothing else

  The error estimation is something we should make greater use of, a
track point with error of 600m is not useful when the editor window is
showing a image that is 100x100 meters. And likewise a Node created in
an editor which has an image resolution of 100meters per pixel should
be marked as such.

Any smart ideas?

--
/Erik

PS I tried using a accelerometer to draw, it's very hard. DS




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