Wonder how much you read and/or understood from my reply...
Just follow my steps to prepare TG2's scene for export and continue with step 8
create a "micro exporter" `(right mouse button -> create other -> micro exporter)
9) double click on it and set the filename to something like "terrain.obj" (it automatically saves it as obj then)
The near and farthest settings control the distance over which TG2 will output the geometry.
The output of the geometry is based on what your render camera sees.
So what also works well is a 90 degrees down facing camera at 0, Y, 0 where Y is an appropriate altitude from where it can "see" the portion of the terrain you want to be exported.
If the altitude of your camera is 1000m then set farthest distance to something a bit bigger, say 1500m. Then all geometry up to 1500m away from the camera will be exported.
10) Once the micro exporter is configured you need to enable the export in the render node, so go to the render node
11) In the last tab, called "sequence/output", you need to enable the micro exporter by clicking on the green '+' sign then choose "assign micro handler" and choose "micro exporter 01". Don't forget to actually activate the output by checking the box to the left.
12) Now your export-camera and mesh export node are configured, all you need is to render your scene and with each render it will automatically save out the mesh. So don't forget to disable it after you're done with exporting, because.....
13) The number of triangles is determined by the render detail setting in the quality tab. For export a detail of 0.4-0.5 results in a nice mesh suitable for animating a camera-path or fluid-sims.
If you render with detail 0.8 or higher, for instance, the mesh will become VERY dense and the exported file will become very large and also will take some time.
These steps should guide you through the whole process...
