Hey Arno! I did some initial test to convert fsx mdl files to the openflight format. Exporting works fine, but when I look at the flt file in the osgviewer (openscenegraph-viewer), the polygon seems to be flipped. Also, the building in my case is mirrored/flipped. Coordinate system problem? I have attached an image: 1. View in MdlConverterX, 2. In osgviewer. Everything is "flipped"