Fishlips' pre-generated terrain files can indeed be converted to T:ANE format, though it's a little bit involved. You need to also have a copy of Trains available which is version 2012 or earlier. First, in 2012, create a new route consisting of one baseboard only (no tracks, textures, terrain, etc.) and save it under the name you ultimately want. Exit from Trainz.
Start Content Manager (again, Trains 2012 or earlier) and open your new route in Explorer. Also, import/open the Fishlips route in Explorer (don't mix up the two windows!). In the Fishlips route, rename the .gnd file (it could be something like columbus.gnd, etc.) to mapfile.gnd. COPY this file into your new route file, so that it overwrites the existing mapfile.gnd. Commit your new route, and revert the Fishlips original.
Now open your new route in Trainz 2012. Save it and the default session created with it and exit.
Again open Content Manager (2012), find your new route and session and select both. Right click on either one and choose Export to CDP. Save it somewhere where you can find it on your hard drive.
Open T:ANE content manager and from the File menu choose Import content files... then locate your saved .CDP file and import it. You can find the newly imported files in T:ANE Content Manager by choosing Today from the list types at the top. If you want to retain the HOG textures (showing roads, rail lines, etc.) right click on the two files (route and session) and choose List Dependencies from the context menu. Download (or import from your 2012 installation) and install any missing dependencies.
In T:ANE your new route and session should show up in your routes listings. If you open them and still find holes in your terrain where a HOG texture should have been, choose Delete Missing Assets from the Main Menu and save, close and re-open. The gaps should be gone, as will the missing HOG texture. There is another thread on the forum that addresses problems resulting from several different sets of HOG textures used in different circumstances, but in any case you'll have the actual terrain at minimum.
You may also find other anomalies, such as high ridges at the edge of a route. In this case just remove the offending baseboards.
No warrenty is implied or given, but it reliably works for me. It's not perfect, and a bit of work, but it does open up use of the huge library of terrain files created by Fishlips and is well worth it, I think.
Lamont