[Windcatcher]

I'm not sure about everything that .3DS supports, but OpenZone's .3DS import expects everything to be composed of triangles.

You're right about RECTANGLE/RECTANGLETEX being quads. The -TEX variants allow you to specify texture coordinates, while the non-TEX ones force OpenZone to use it's own algorithm to guess at decent texture coordinates. Obviously, if you're importing from an external source, I strongly recommend using the -TEX variants. The non-TEX ones are mainly for OpenZone's use since many of its scripts don't generate texture coordinates and have to rely on its internal algorithm.

All of my 3D software use OpenGL, which requires that textures be a power of 2 on each side. They don't have to be square, but they have to be, for example, 64, 128, 256, 512, etc. on a given edge.

KhaN has taken the route of modeling entire zones and then importing them as a giant .3DS file. It's possible, but has some minor limitations. The main one is that the .3DS format doesn't have a way of setting the "masked" and "solid" flags I mentioned above, so it means setting them after the import. These flags are critical for objects like trees where solid has to be set to FALSE so players don't bump into their leaves (and the masked flag is critical so the masked-out parts of the textures will be transparent). The new features in OpenZone 5.6 under Edit Polygon Properties should make those easier (until then, the only real way was to do a search-and-replace on the .SCN file to set the flags for a given texture).

Importing entire zones also means that OpenZone doesn't know which mesh is the "ground" mesh, so if you place objects in the zone after importing it, OpenZone might have trouble keeping them on the ground (when OpenZone generates its own ground it can make sure that trees, for instance, always adhere to the ground). It's not an issue if you don't plan on adding anything from OpenZone's internal library after you import your zone or, if you do, if you plan on placing objects precisely.

If you only want to import and immediately export to .S3D, then the only issue is the "solid" and "masked" flags (and possibly the transparent/semitransparent flags), which can globally be set for a given texture from the Edit Polygon Properties dialog.