Home > Supported File Formats > U3D to OBJ

How to convert U3D (Universal 3D, 3D PDF) 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.

U3D

U3D is a semi-obsolete 3D mesh file formats from the 2000-2009 era of the 3D graphics world and whose history is little understood outside the confines of a few 3D graphics companies. Even so, U3D is still a fine 3D file format as a pipeline to get 3D data embedded within 3D PDF files, especially with the full and extensive implementation made by Okino.

For more details on the U3D file format, its core features and limitations, how to embed U3D files within 3D PDF files and the features of the Okino U3D import/export converters, please refer to this WEB page.

Generally speaking, U3D was implemented by a few 3D companies in the mid to late 2000s when it was pushed by Adobe+Intel as part of the line of 'Acrobat-3D' software packages. In very loose terms, U3D is used to convey and embed 3D model data within 3D PDF files, where PDF would be the container for the 3D data.

U3D started off in the 1990s as Intel's "IFX" gaming toolkit which was than thrust upon Macromedia, Alias Research, Softimage and other similar companies around the year 2000 to be accepted as a new "industry standard" 3D file format called "Shockwave-3D". The dotCOM bubble caused SW-3D to die pre-maturely after 2001 only to be rebranded as U3D or the "Universal 3D file Format" in 2004 (ECMA-363). Its specification PDF document described it as "An extensible format for downstream 3D CAD repurposing and visualization". However, U3D was highly profit/sales motivated/biased and not consumer/end-user motivated. As such, partly due to the 2008/2009 recession, those companies and their investments in U3D died away.

Okino is and was critical of U3D back in the day as it was the company which created the main conversion implementation of U3D for both import and export. It understood the limitations of U3D well and of its false promotion as a "universal file format" whose title should really have gone to those such as COLLADA, FBX, VRML2, etc. When implemented well U3D is a fine file format by itself but few companies invested enough time and money to support U3D import and export in a most ideal manner.

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.

Limitations of the U3D File Format

U3D import converter's overview

OBJ export converter's overview