3DS Max 2012 OBJ file import missing polygons

Question

I started learning OpenGL. I got to a point I want to import some "real" objects. After "Googling" I decided I will go with OBJ file for start, since it is simple to understand, and there are plenty of tutorials on how to read them properly.

I have from university access to 3DS Max 2012. So I tried to create very simple model (just deformated cube) and exporting it using OBJ file, just to vertices and triangles for the moment, without textures, so I can examine its structure by myself. But if I imported it right back to 3DS from OBJ file, now it renders somewhat strange, like its smoothen, and with lightsource, even I have none in scene. But the geometry, its wireframe is intact.

So I thought maybe it is problem of exporting only vertices and triangles so I downloaded Enterprise-D model from internet, exported with everything on (normals, textures everything), and again imported it. Now, some polygons are missing.

So, I want to ask, am I doing something terribly wrong, or is there some incompatibility issue between .max and .obj file ? Even it is only simple textured model without any lightsources, animation etc.? Thanks.

Edit: I tried objects with MeshLab, the first, deformated cube was absolutelly OK. But still bothers me that 3DS Max doesen´t render it properly. In Enterprise-D model, there are polygons missing even in MeshLab. I uploaded rar archive with .max model of Enterprise, same .obj model exported from 3DS, and obj model of deformated cube. Download here (2.5 MB, filesonic).

Answer 1

The first problem you described sounds like the normals getting smoothed. I notice your Test.obj file was exported without normals; when it was re-imported, 3DS would auto-generate normals for it and probably assumed they were to be smooth. In this case exporting with normals should fix the problem.

As for the Enterprise model, I opened it in Maya and saw some odd-looking, possibly malformed faces on the bottom, but no actual holes that I could find. Are you sure the problem is not with the original model?