OpenStreetMap Forum

adrian2012

Member

Registered: 2013-07-05

Posts: 2

Gpx WGS84 OSGB36

Hi everyone,

Im getting to grips with my new etrex 20 and making waypoints for it.

I was looking in to the GPX format and there does not seem to be anything that specifies which map datum you are using, eg. WGS84 or OSGB36.

For example: Kingshouse in Glen coe would be

<wpt lon="-4.84105015" lat="56.65135193">
  <name>Kingshouse</name>
</wpt>

How does the etrex (or any gps device) know what format the lon/lat uses? I know that the etrex can change the settings on the device to display grid refs/different coordinate systems but surely this should be specific to the gpx files espcially if you have loaded multiple gpx files using different systems?

Thanks - would appreciate any thoughts on this!
Adrian

Last edited by adrian2012 (2013-07-05 21:05:25)

RetiredInNH

Member

From: Thornton, New Hampshire

Registered: 2010-02-11

Posts: 73

Website

Re: Gpx WGS84 OSGB36

From Basic GPS Capture, Edit, and Navigation Using A Garmin GPSMAP76CSx:

Garmin GPS receivers capture and store positions as decimal degrees of latitude and longitude referenced to the WGS84 datum. Although users can set how GPS positions are displayed on-screen, those settings have no effect on how the GPS positions are actually captured, or stored, internally.

I believe that this is not Garmin specific but is, in fact, part of the GPX standard.

Added later:

I have checked the GPX documentation and indeed it states:

The latitude of the point. Decimal degrees, WGS84 datum.

Last edited by RetiredInNH (2013-07-05 22:21:42)

Bernhard Hiller

Member

Registered: 2011-05-10

Posts: 1,122

Re: Gpx WGS84 OSGB36

Hm, I am also not fully sure about the datum to use. I often write the values shown in Google Earth down and then create such WayPoints in a GPX file to be transferred to my Oregon - and it works correctly!  You can also set the symbol, e.g.
<wpt lat="36.513" lon="30.056"><name>Arykanda</name><sym>Flag, Red</sym></wpt>

adrian2012

Member

Registered: 2013-07-05

Posts: 2

Re: Gpx WGS84 OSGB36

Thanks for the replies and for digging out that information. Good to know how the Garmins store coordinates -

It does look like that solves my problem - as the GPX docs specify that the coordinates are all WGS84 all software should interpet as such - something to check when making the files!

Thanks again,
Adrian