OBJ is a text mesh-interchange format. Faces refer to vertex positions and can also refer to texture coordinates and normals. Material definitions and texture images commonly live in separate files, so an OBJ filename alone does not imply a self-contained visual asset.
- Geometry
- Indexed polygon faces; the supported importer triangulates simple planar polygons.
- Units
- No reliable physical unit is supplied by the supported geometry subset.
- Appearance
- MTL files and textures can describe appearance, but this workbench does not load them.
- Structure
- Object/group labels identify geometry boundaries; these are not parametric features or a CAD assembly tree.
Choose an output for shape or scene interchange
OBJ→STL is appropriate when the next application needs triangles and the material appearance can be discarded. OBJ→GLB packages supported geometry into a single scene-format file with an explicit scale. Neither conversion here includes an MTL/texture bundle.
Physical size needs a deliberate choice
Before OBJ→GLB or OBJ→3MF, choose millimetres, centimetres, inches or metres to describe the source coordinates. GLB scales them into metres; 3MF declares the selected unit. A label in a filename is not a trustworthy automatic scale detector.