[GRASSLIST:6292] Re: GPS points off by about 120m to the west

[Dylan Beaudette]

On Mar 29, 2005, at 11:58 PM, Hamish wrote:

>> 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
>
>

Hamish and others who replied,

thanks for the information on this -- i was using v.in.ascii to import 
these points ... thinking that the GPS would be exporting my points in 
NAD83/UTM as the GPS unit was configured to use. i will give it a try 
with the CVS copy of v.in.garmin a little later this week.

on a related note, if i am sending points to the GPS- they would need 
to be transformed to WGS84 as well?
maybe cs2cs can do this for me?

thanks!

--
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341