[gdal-dev] GDALwarp Mercator to UTMs

[Geoff Shipton]

Good day, almost a complete newbie here but making progress!

I have followed all the examples of GDALwarp with some success and also 
been able to use GDAL_translate to take an image with no geoferenced 
info and generate a UTM GeoTIFF (including screens from Google Earth)

However my ultimate aim is to take a Mercator chart and generate a
background image as a UTM GeoTIFF, this so far has eluded me!

I have a Mercator Chart with the known corners in Lat/Long coordinates 
degrees, but I can't find a suitable EPSG/Proj4 projection that allows 
the use of Lat/Long degrees to designate -a_ullr for GDAL_translate.  
The following almost works:

GDAL_translate -a_srs WGS84 -a_ullr -45 78.5 45 53.5 <source tif> <merc 
geotiff)
then:
GDALwarp -t_srs EPSG:32631 <merc geotiff> <UTM geotiff>

But of course the result still has unequally-spaced lines of Latitude 
because the WGS84 input to GDAL_translate assumes the "google earth" 
type projection...not Mercator

Any ideas are very welcome - I have been circling this problem for 
several days.

Geoff