I have been doing some more testing with 32-bit EXR heightfields, as well as 32-bit Tiff heightfields and has discovered a few things. I think Oshyan mentioned it before, but older versions of Photoshop like CS5 don't properly save 32-bit exr files. The exr files get clamped at 16-bit levels for some reason, so when loading on in as a heightmap in terragen the max height for the heightfield will show as 65.5 km, which I think relates to the max channel value of
65536 in 16-bit images. I did try saving the same 32-bit exr as a 32-bit grayscale tiff out of Photoshop CS5 and that worked perfectly in Terragen as a heightfield.
erx-io as mentioned is a plugin that supports saving 32-bit exr's with a bunch of options and that does properly save the 32-bit exr for use as a heightfield in Terragen.
Another interesting thing I discovered is the "Height range" displayed at the bottom edge of the Heightfield load shader is very useful for knowing how much elevation data is in your heightmap. With an 8-bit heightmap the max value you will see there is 256m (0-255 channel values) and for 16-bit heightmaps you will see up to 65.5 km (0-65536) and for 32-bit heightmaps you can see values beyond 1.03e+003 km (0-1,024,000 +).
Not that I would recommend doing this for any reason but just because I was curious I made a heightmap with such a huge range I had to use a displacement multiplier of "0.00000000000000000000000000000000001" to get my heightfield to the appropriate height within the terragen camera view. The range for that 32-bit heightmap was "min = 0 mm, max = 3.4e+032 Mm".
Well, glad I got that figured out.
-Derek