FWIW: I tried converting the gpx files from WGS84 to NAD27 and using the geotiffs with those tracks under viking. That still didn't work, even though the gpx transforms looked correct.
That may be because NAD27 uses a different ellipsoid, so converting coordinates that are in NAD27 but treated as WGS84 to WGS84 UTM does not give you the NAD27 UTM coordinates. IIRC this effect is bigger than the actual surface datum shift in meters. I have the gpsbabel scripts I used for that if any one is interested. Basically one has to use gpsbabel to convert to unicsv and then make a new unicsv with the datum transform then conver the unicsv back to gpx. So, next I tried converting the World File (tfw) for the geotiff from NAD27 to WGS84. That seems to work. So then you have the geotiffs georeferenced in WGS84. But, it is lined up with the NAD27 UTM grid instead of the WGS84 UTM grid. That's probably not detectable. I had been thinking about how to do this right, within viking. Transforming the way the map lines up makes more sense, since then you can alpha composite with other maps. So, having a projection selector for georeferenced maps and transforming the origin of the world file on read seems like a plausible approach.
pgpoSJVa52QAd.pgp
Description: PGP signature
------------------------------------------------------------------------------ Achieve unprecedented app performance and reliability What every C/C++ and Fortran developer should know. Learn how Intel has extended the reach of its next-generation tools to help boost performance applications - inlcuding clusters. http://p.sf.net/sfu/intel-dev2devmay
_______________________________________________ Viking-devel mailing list Viking-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viking-devel Viking home page: http://viking.sf.net/
