About File Formats & Downloading

Downloading Models

     All of the model files at the Large Geometric Models Archive have been compressed using the "gzip" program, and the file names have been appended with the suffix ".gz". You will need the program "gunzip" or a similar tool in order to recover the uncompressed polygon files.

     Many Web browsers will allow you to download a polygonal model simply by clicking on the appropriate download link. However, some browsers have the default behavior of uncompressing a file with the ".gz" suffix and then attempting to display the result as an HTML page. If this is the case with your browser, you will need to find another option that will give you a dialog box that allows you to specify a location at which to store the file on disk. For Netscape, holding down the "Shift" key and left clicking on the file link will pop up this dialog box.

Polygon Model Formats

     We have provided each model in at least two different polygon file formats, Inventor and PLY. We describe each of these below in more detail.

PLY Files

     The PLY file format is a simple description that was designed as a convenient format for researchers who work with polygonal models. There is both a text and a binary PLY file type, but all of the PLY files at this site are text files. For more information about the PLY file format including code to read, write and manipulate files, visit our PLY page. With the code that we have provided, you can probably add a PLY file reader to an existing polygon manipulation program in an hour or less.

Inventor Files

     The Inventor files at this site are all text files. The polygonal object files that we provide are what is known in Inventor as an Indexed Face Set. This means that each vertex in a model is listed once, and each vertex consists of (x,y,z) coordinates and possibly surface normals. Each polygon is simply a short list of indices into the list of vertices. Because Inventor describes objects as general directed graphs, an Inventor file typically contains several levels of nested keywords, braces and brackets.

     Because it is an open standard, there are many tools that read and display Inventor files. Moreover, the Inventor file format is very closely related to the VRML file format, so an Inventor file may be easily converted to VRML.

VRML

     For some of the polygon files, we have also provided a small VRML file of the given model. These VRML files do NOT contain the full-sized models. Rather, they are simplified version of the models that will allow you to get a rough idea of the 3D shape of the full models.