I am getting incorrect normals from CAD Assistant when converting STEP files to OBJ. I experience the same in my own program using OCCT 7.5.0, that read STEP files and render them directly using OpenGL. My program do take in account the orientation, transformation and triangle indexes of the shapes and faces.
When loading a STEP file into CAD Assistant the viewer seems to fix the normal direction, but when I convert it to OBJ I get incorrect normals.
This is just one example, I can replicate this with various STEP files and viewers (STEP and OBJ files are attached in .zip):
- Correct normals from STEP file in CAD Assistant viewer.
- see attached picture: SpaceShuttle_STEP_loaded_into_CAD_Assistant.PNG
- Incorrect normals when converted STEP to OBJ using CAD Assistant and viewed in MeshLab, Autodesk Viewer, my own viewer etc.
- see attached picture: SpaceShuttle_STEP_exported_as_OBJ_from_CAD_Assistant_viewed_in_MeshLab.PNG
- Incorrect normals when reading STEP using OCCT and rendered using OpenGL.
- see attached picture: SpaceShuttle_STEP_read_using_OCCT_and_rendered_using_OpenGL.PNG
Seems like this is a general issue in OCCT, are the orientations read from STEP files not correct? How does the CAD Assistant viewer fix the normals?
Best regards, Oliver