[GRASSLIST:6285] Re: GPS points off by about 120m to the west

[Hamish]

> after retrieving some waypoints from my Garmin 12 GPS, i noticed that
> when  imported into GRASS, they were offset by about 120 meters to the
> west....!
> 
> here is a picture of the bad (red) points, and corrected (blue)
> points: http://basho/~dylan/temp/bad_gps.png
> 
> 
> i am nearly positive that the data in GRASS is good: in NAD83/WGS80
> UTM zone  10N projection.
> 
> the GPS was set for the same projection parameters...
> 
> any ideas on what could have caused this 120meter shift to the west? 
> 
> could my GPS really be in a NAD27 datum, and still be reporting NAD83
> ? 


The GPS is exporting waypoints in WGS84;
the error you are seeing is surely due to a datum shift;
v.in.garmin should take care of all that for you.

i.e. regardless of what you have the GPS datum set to display on the
screen, it will output WGS84. At least that what my Garmins do.

were you importing with v.in.garmin or v.in.ascii?


note v.in.garmin in 6.0 is broken, get the latest version of the script
from CVS.



Hamish