Create a terrain model in your favorite 3d modeling app (<ahref="http://www.blender.org/">Blender</a>, <ahref="http://www.earthsculptor.com/">Earth Sculptor</a> or any other, which can save a model to Wavefront .obj format)<br/>
Use <strong>File -> Import -> Terrain from Wavefront .obj</strong> action to import it as sectors. Each polygon in your model will be transformed into sector.</p>
<strong>Limitations:</strong><br/>
The model should be triangulated.<br/>
Polygons should not overlap each other when viewed from the top.<br/>
<strong>UDMF only</strong>, because the mode uses vertex height offsets to create sloped floors ("zfloor" vertex field).