Simple Shape won't help you. You need to constrain the export area. Since you can't do this with the Geog Heightfield Shader itself, you have to use a sneaky workaround. I'm pretty sure it will work, but no guarantees of quality, etc. You'll just have to try it. So...
Take your scene with the geog Heightfield in it, now below it in the network add a Heightfield Generate. Then, feed the output of the Heightfield Shader that the Geog Heightfield is plugged into, feed that into the Shader input of the Heightfield Generate. You're connecting a *red* node to the input port of a *green* one here, that's critical. And it has to go into the Shader input, on the right side, not the generic "Input" one on the left. Then, move the heightfield to the center of the area you want to export, then set the size of the heightfield *in meters* (not "number of points") to cover the area you want to export. Basically you're moving this new, second heightfield, and using it as a sort of bounding box for your heightfield export. Then, set the Number of Points to be one of those power-of-two+1 variants I listed above, click Generate, and then you can do the Save As routine on it as before. That *should* get you a heightfield that is *just* the area you wanted to export.
Vector Displacement, any displacement applied to the terrain, can be saved as TER. BUT BUT BUT, you will LOSE overhangs and any non-planar features, AND you have the potential/likelihood of losing resolution/detail. Try it, if you get good results then great, but don't *expect* good results. It is *not* a workflow I would recommend.
Instead, IF your v-disp is planar, i.e. no overhangs, then it's essentially a heightfield already. Export it as an image format, import it into TG, save as TER (or import it into any terrain app that supports standard image formats). In other words if you are actually having to use vdisp, you probably can't accurately reflect the features in a heightfield, because the whole point of vdisp is it gets you non-planar features.
- Oshyan
