I'm almost embarrassed to ask this as I'm sure that there is probably a very simple answer that I'm overlooking...
I created a terrain in World Machine 2 along with color and flow map images. I imported the .ter file into TG3. The terrain looks great, but... I can not for the life of me seem to figure out how to apply the color image to the terrain. Any pointers on how to resolve this (hopefully basic) issue?
You'll have to set up the image shader to project x,z at the same size and position as your .ter. I sometimes use the Heightfield Resize to get the .ter to be a specific size like 1k square to make both image and displacement line up.
Use an Image Map shader to load the output images. You'd use Plan Y projection actually, and change size to be the same as the heightfield (size is measured in meters). Heightfield Load nodes now display heightfield size at the bottom "XY Size", and you can just use the same values in your Image Map Shader size fields. Then you just need to set the same position. By default Heightfield Load uses Position Center while Image Maps use Position Lower Left, so you'll want to change one of those to make it easier to align. As long as they're using the same position reference, they should line up with equal sizes.
To use the base texture, your Image Map Shader should be added in the Shaders layout and just be part of the regular shading chain (it would come after Base Colours in the default scene). For flow maps and the like, you'd want to use them as a Mask Shader or similar affector (e.g. Fractal Breakup) for other surface shader nodes.
Thank you! I appreciate the help on this.