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How to convert STL (StereoLithography) to OBJ (Wavefront .obj,.mtl)?

PolyTrans|CAD+DCC performs mathematically precise CAD, DCC/Animation, GIS and BIM 3D file conversions into all key downstream 3D packages and file formats. Okino software is used and trusted throughout the world by many tens of thousands of 3D professionals in mission & production critical environments, backed by respectable personal support directly from our core development team.

STL

STL (StereoLithography) is one of the industry's oldest (and simplest) 3D file formats created back in 1987 for 3D Systems' first commercial 3D printer. It is widely used for rapid prototyping, 3D printing and CAM. Okino has provided one of the very first and still primary STL export conversion systems for close to 3 decades.

Please take note that there is no 3D file format which is much simpler than STL. It is not a high-end, high fidelity 3D conversion file format as many people have come to wrongly believe. Rather, STL defines just a raw triangulated polygon mesh with no smoothing information (vertex normals), no uv texture coordinates, no assembly hierarchy part naming or any material assignments. 3MF and VRML2 are often much better file formats for moving 3D datasets into downstream programs and/or 3D printers.

The Okino STL exporter WEB page provides good graphical tutorial about how to convert CAD file data into STL and also how to clean a 3D model which is 'almost water tight'.

OBJ

Wavefront OBJ is a little understood but highly used and prevalent 3D "polygonal mesh" file format used throughout the 3D graphics world. Okino, Alias Research and McNeel made it popular in the early to mid 1990s as a general purpose, simple-to-read, storage and transmission 3D file format, especially for the then-new companies who began to sell 3D mesh models via the Internet.

Relatively speaking, OBJ is a rather simple file format but a bit better than STL although similar to the more modern 3MF format.The OBJ format allows for 1 or more unique polygonal mesh objects to be defined, each with optional UV texture coordinates and vertex colors. Material definitions can be linked to the mesh geometry as defined in the separate 'MTL' file. The material definitions are rather simple (ie. no PBR material support) but acceptable, and with varied levels of texture mapping support. OBJ format does not provide support for object hierarchy, local transformations, meta data, lights, cameras, skinning or animation. Most notably, OBJ does not allow for 'object instancing' and hence 1000 copies of a screw would be saved to OBJ as 1000 explicit copies, rather than 1000 references to one master object.

A short history: In the 1980s there was a program called Wavefront Visualizer which ran on UNIX and ran its early rendering pipeline as a series of tee'd command line 'applets'. The data flowed from one applet to another via various ASCII based files - OBJ for geometry, MTL for materials and other ASCII files for animation, skinning, deformation, etc.

Okino knows of the Wavefront OBJ file very well as it provides the one and only full implementation of the OBJ file format and with the ability to consume exceedingly large OBJ files quickly and efficiently. This includes the only known implementation of OBJ-centric 'NURBS geometry' (surfaces and curves) within the OBJ file format (which is little or not used) other than that from the McNeel Rhino-3D software.

How to Convert CAD to STL

STL import converter's overview

OBJ export converter's overview