Hi Dan,
You can also use images that are not GeoTIFF, but in that case you will have to provide all placement information in the INF file for resample. When using GeoTIFF images that is not needed, so that makes your life a lot easier.
All input for resample does indeed have to be WGS84, as that is the projection used by FS. So if your data is in a different format, you will have to reproject your images. I use the gdalwarp tool for that (comes with
GDAL). In the same package is also the gdal_translate tool, which I used to make my own GeoTIFF images from the BMP images I had.
That is indeed a GeoTIFF image. I tried to convert it with gdalwarp to WGS84, but I am not really familiar with NAD83, so I could not find all correct parameters yet.
One thing I noticed when I used my own GeoTIFF images with resample, is that resample does not all all GeoTIFF formats. The TIFF file can be band seperated or not, and one of those two do not work (an error is thrown). I always forget which of the two works though
.