[OSM-talk] Datums

[David Earl]

> -----Original Message-----
> From: talk-bounces at openstreetmap.org
> [mailto:talk-bounces at openstreetmap.org]On Behalf Of Andy Robinson
> Sent: 15 January 2007 09:45
> To: 'Andrew Rowbottom'; talk at openstreetmap.org
> Subject: Re: [OSM-talk] Datums
>
>
>
> Andrew Rowbottom wrote:
> >Sent: 15 January 2007 9:36 AM
> >To: talk at openstreetmap.org
> >Subject: [OSM-talk] Datums
> >
> >Can anyone tell me what Datum I should be using on my GPS? I can't
> >seem to find anything on this in the Wiki.
> >I'm assuming I should be using WGS84 since that's reasonable for the
> >whole world, but obviously in the UK (where I am) my datum would
> >normally be OSGB(36?). The difference is between 70 and 100 meters
> >which is significant compared to current GPS accuracy.
>
> OSM takes latitudes and longitudes and therefore is working in WGS84,
> however I don't think it generally matters what your GPS is set to use for
> its displays, My GARMIN still dumps out files in the WGS84 lat/lon format
> regardless of what I'm doing or which datum I'm using for the display.

Even if it didn't, GPX is defined as being in WGS84, so if the starting
point is, say, reading a GPX file into JOSM, anything creating such a file
would presumably have to do a conversion to WGS84. (I had assumed it was the
reader that was converting, but I've not looked at the raw data coming out
of the GPS).

David