Wavefront .obj file

Object files define the geometry and other properties for objects in Wavefront's Advanced Visualizer. Object files can also be used to transfer geometric data back and forth between the Advanced Visualizer and other applications. Object files can be in ASCII format (.obj) or binary format (.mod). This appendix describes the ASCII format for object files. These files must have the extension .obj. In this release, the .obj file format supports both polygonal objects and free-form objects. Polygonal geometry uses points, lines, and faces to define objects while free-form geometry uses curves and surfaces. The .obj appendix is for those who want to use the .obj format to translate geometric data from other software applications to Wavefront products. It also provides information for Advanced Visualizer users who want detailed information on the Wavefront .obj file format. If you are a 2.11 user and want to understand the significance of the 3.0 release and how it affects your existing files, you may be especially interested in the section called "Superseded statements" at the end of the appendix. The section, "Patches and free-form surfaces," gives examples of how 2.11 patches look in 3.0. Most of this appendix describes the different parts of an .obj file and how those parts are arranged in the file. The three sections at the end of the appendix provide background information on the 3.0 release of the .obj format. The curve and surface extensions to the .obj file format were developed in conjunction with mental images GmbH&Co.KG, Berlin, Germany, as part of a joint development project to incorporate free-form surfaces into Wavefront's Advanced Visualizer. Reads the contents of the specified .obj or .mod file at this location. The call statement can be inserted into .obj files using a text editor. filename.ext is the name of the .obj or .mod file to be read. You must include the extension with the filename. will work as expected. For more information on the scmp statement, see appendix C, Variable Substitution for more information. Using this method, the scmp statement provides the .pv file for all subsequently called .obj or .mod files. Executes the requested UNIX command. If the UNIX command returns an error, the parser flags an error during parsing. The vertex data is represented by four vertex lists; one for each type of vertex coordinate. A right-hand coordinate system is used to specify the coordinate locations. When vertices are loaded into the Advanced Visualizer, they are sequentially numbered, starting with 1. These reference numbers are used in element statements. Specifies a geometric vertex and its x y z coordinates. Rational curves and surfaces require a fourth homogeneous coordinate, also called the weight. The usage determines how many coordinates are required. Special points for curves require a 1D control point (u only) in the parameter space of the curve. Special points for surfaces require a 2D point (u and v) in the parameter space of the surface. Control points for non-rational trimming curves require u and v coordinates. Control points for rational trimming curves require u, v, and w (weight) coordinates. Vertex normals affect the smooth-shading and rendering of geometry. For polygons, vertex normals are used in place of the actual facet normals. For surfaces, vertex normals are interpolated over the entire surface and replace the actual analytic surface normal. There are three steps involved in specifying a free-form curve or surface element. o Specify the type of curve or surface (basis matrix, Bezier, B-spline, Cardinal, or Taylor) using free-form curve/surface attributes. o Describe the curve or surface with element statements. o Supply additional information, using free-form curve/surface body statements The next three sections of this appendix provide detailed information on each of these steps. All curves and surfaces require a certain set of data. This consists of the following: