[GRASSLIST:2240] Re: Importing a NAD83 map into a NAD27 location.

[Markus Neteler]

On Wed, Jan 14, 2004 at 06:59:30AM -0500, Ben Logan wrote:
> I have some data which uses the nad27 datum (the spheroid is clark66)
> and I created a location based on that.  However, I now have some
> raster maps of the same area which I need to import, and they use
> nad83 (with the grs1980 spheroid).  All the data is UTM zone 17.  Is
> this a problem?  Do I need to do something to convert the new data?
>

IMHO it's not the same:

cs2cs -le | grep -i "clr\|grs"
    GRS80 a=6378137.0      rf=298.257222101 GRS 1980(IUGG, 1980)
    GRS67 a=6378160.0      rf=298.2471674270 GRS 67(IUGG 1967)
   clrk66 a=6378206.4      b=6356583.8      Clarke 1866
   clrk80 a=6378249.145    rf=293.4663      Clarke 1880 mod.

compare clrk66 and GRS80.
Also NAD27 != NAD83.

So you would need two different locations and reproject.
The 5.3-CVS version of r.in.gdal will test and omit to import
maps if ellipsoid/projection/datum do not match. However, this
test is not implemented in 5.0.3.

Markus