OBJ

OBJ is a geometry definition file format developed by Wavefront Technologies, used to store 3D model data in a plain-text ASCII format and widely employed as an interchange format between modeling, rendering, and animation software. An OBJ file describes the vertices, texture coordinates, vertex normals, and faces that compose a model. Data appear as lines starting with keywords such as v for vertex coordinates, vt for texture coordinates, vn for vertex normals, and f for faces. Faces reference indices of the preceding elements, typically using 1-based indexing, with a syntax like f v1/vt1/vn1 ... . The format also supports grouping with o and g, applying materials with usemtl, and smoothing with s. Additional lines may specify parameters or comments marked by #.

Materials for OBJ models are defined in a separate MTL file, linked by an mtllib directive. The MTL file specifies material properties such as ambient, diffuse, and specular colors, shininess, and texture maps via tokens like Ka, Kd, Ks, Ns, and map_Kd. OBJ itself does not embed shading models; it relies on the material definitions in the associated MTL file and the rendering system to interpret them.

OBJ originated in the 1980s with Wavefront’s tools and became an industry standard due to its simplicity and broad tool support. It remains popular for workflows requiring straightforward geometry interchange between modeling packages (such as Blender, Maya, and 3ds Max) and game engines or renderers. Limitations include lack of animation data, scene graphs, or metadata beyond basic geometry and materials; no explicit units or coordinate system; and reliance on external MTL files for materials, which can lead to inconsistencies across tools.