I believe you also wrote an email to support, but since others might be interested in the info I'll just reply here publicly.
Terragen currently has somewhat limited export functions. It is designed as a procedural environment modeling and *rendering* application. We are working toward better export functions, but the primary focus to this point has been on use of Terragen-generated content within Terragen itself, with the import/export functions designed to augment that and allow Terragen output to be used with other "offline" render functions.
Currently what you can export easily are:
1: A spherical environment or skybox. This could be just the sky, since it is distant and doesn't need to be interacted with in most cases, or it could include terrain, if desired.
2: Terrain as a heightfield, without texturing. This can be done only for non-procedural terrains by default (i.e. a Heightfield node), but you can easily convert any procedural terrain into a heightfield by using the Shader input on a Heightfield Generate node. Note that exporting as a heightfield inherently loses any non-planar (e.g. overhanging) features of the terrain.
3: Terrain as geometry using a Micro Exporter node. This exports terrain directly from the rendering process, and so it is not optimized for use in other applications and requires some work to make it more usable. It also is best to export using a single thread to avoid tile edge issues. There is more discussion of this elsewhere on the forums and the Micro Exporter is covered in our Wiki documentation:
https://planetside.co.uk/wiki/index.php?title=Micro_Exporter4: Terrain as Vector Displacement. This is one of the most accurate ways to go, but it does require some setup and expertise, and your engine may not support the output directly. Here's a video tutorial:
https://www.youtube.com/watch?v=bTKfAeEPDhYThe FBX export you probably tried (from the File menu) is only intended to export Camera, Lights, and animation data, it does not export any geometry. Full scene export is not likely to be possible any time in the near future. Texture export may become an option in addition to the above-mentioned terrain export functions, but for now if you want textures you'd have to render a top-down orthographic view at high resolution with neutral lighting.
If you have access to Maya there's also Terraman which makes some of these things easier for getting into Maya, at least:
https://www.highend3d.com/maya/script/terraman-for-mayaAll of this is discussed in various other threads here on the forums and I suggest you do some searches to get more details. For example Vector Displacement is discussed at length here:
https://planetside.co.uk/forums/index.php/topic,21311.0.htmlAnd in several other threads.
- Oshyan