By virtue of using GDAL's auto-detection, TB already supports .BT files (and Terragen .TER, etc). You can force it to use them by selecting "All Formats" in the open file dialog.

I've opened Terragen files this way, and they work perfectly because they don't have georeferencing information.

However, .TB files do contain georeferencing.

The only thing stopping .TB support as far as I can tell is this issue:

http://feedback.arma3.com/view.php?id=18081

The GDAL library is v1.6 the latest is v1.8

An update would enable us to use source L3DT (32bit) files straight from our project folders among other improvements.

Thank you for kindly assigning this task.

well migrating to a new GDAL would be quite difficult - for your information upgrade from 1.5 to 1.6 took more than a week in the past. About L3DT,.BT, etc. GDAL is one thing, but unless providing proper libraries in addition it won't be able to load those advanced formats. And problem with additional libraries is in a fact, that many of them are not distributed under a compatible licence(like GNU/GPL,..)

BT support is not relevant anymore, this ticket can be closed.