The main purpose of the file is to specify an area for which other specialized programs automatically create digital elevation model or download surface map from map server. One such program might be included in future therion (as an xtherion plugin perhaps).
Kind of like 'Therion Earth', nice. I can see why you have started with lat long co-ords now, probably a good move. I thought I might use bbox as a guide when creating terrain models with terraintool to use with Loch, 'Therion Earth' the manual way. It is not absolutely necessary though, as I seem to have managed perfectly well until now. However, using a local epsg co-ordinate system means that the therion user can stick with a consistent system (or at least a number of systems specified by the user) throughout for inputs, and outputs. Currently I think bbox is the only output that goes against this precedent. Bbox is perfectly fine how it is, but maybe as a low priority future addition, add an 'export map' option (for bbox only?) of -coords [<latlong>|cs] with <latlong> being the default and the cs value telling therion to convert to the cs specified in the thconfig file. Bruce