File formats
OBJ
Wavefront OBJ
Definition
OBJ is a widely supported 3D geometry format that originated with Wavefront's Advanced Visualizer. In practice it is used to exchange polygon meshes with texture coordinates and materials, not engineering geometry.
Also known as: Wavefront OBJ, .obj
Updated
Polygons and free-form#
The OBJ specification supports both polygonal geometry, made from points, lines, and faces, and free-form curves and surfaces. Almost every tool that exports OBJ today writes only the polygon part, often with a companion .mtl file for materials.
Because of that, an OBJ from a CAD or AI tool should be treated like an STL: a mesh for rendering or printing, not a model to dimension or edit.
Sources
Related terms
Mesh
A mesh represents a shape as a surface of small flat polygons, almost always triangles, joined at shared edges and vertices. Meshes work well for rendering, games, and 3D printing, but they have no true faces, edges, or exact curves, so they are hard to dimension or edit as engineering geometry.
glTF
glTF is a Khronos Group format for delivering 3D scenes and models efficiently to web and real-time applications. It stores meshes with materials, textures, and animation, which makes it good for viewers and previews but not for engineering edits.
STL
STL is a simple mesh file format that stores a surface as a list of triangles, each with a normal and three vertices. It is the long-standing default for 3D printing, but it has no units, colors, or exact geometry.