==== I imported a kitchen cabinet model from SketchUp to Actif3D. In A3D, some wooden faces of the cabinet is invisible when my camera move to a given angle. Why my model looks OK in SketchUp but some faces are invisible in Actif3D? ====

The problem is SketchUp allow a single side UV map can be displayed just like it is double-sided. In this case, you have to go to SketchUp, right click to the wrong faces, and choose "Reverse Faces" from ne menu.

See this video:

{{youtube>erf2f9s-BZs?full&autoplay}}