OFF (file format)

OFF (Object File Format) is a geometry definition file format containing the description of the composing polygons of a geometric object. It can store 2D or 3D objects, and simple extensions allow it to represent higher-dimensional objects as well. Though originally developed for Geomview, a geometry visualization software, other software has adapted the simple standard.

Composition
The composition of a standard OFF file is as follows:


 * First line (optional): the letters OFF to mark the file type.
 * Second line: the number of vertices, number of faces, and number of edges, in order (the latter can be ignored by writing 0 instead).
 * List of vertices: X, Y and Z coordinates.
 * List of faces: number of vertices, followed by the indexes of the composing vertices, in order (indexed from zero).
 * Optionally, the RGB values for the face color can follow the elements of the faces.

The four-dimensional OFF format, most notably used by Stella4D, which allows visualization of four-dimensional objects, has a few minor differences:


 * First line (optional): the letters 4OFF to mark the file type.
 * Second line: the number of vertices, number of faces, number of edges, and number of cells, in order (the number of edges can be ignored).
 * List of vertices: X, Y, Z and W coordinates.
 * List of faces: number of vertices, followed by the indexes of the composing vertices, in order (indexed from zero).
 * List of cells: number of faces, followed by the indexes of the composing faces, in order (indexed from zero).
 * Optionally, the RGB values for the cell color can follow the elements of the cells.

Comments are marked with a pound sign (#): these are not read by the software.

Example
OFF 8 6 12 1.0 0.0 1.4142 0.0  1.0 1.4142 -1.0  0.0 1.4142 0.0 -1.0 1.4142 1.0  0.0 0.0 0.0  1.0 0.0 -1.0  0.0 0.0 0.0 -1.0 0.0 4  0 1 2 3  255 0 0 #red 4 7 4 0 3  0 255 0 #green 4 4 5 1 0  0 0 255 #blue 4 5 6 2 1  0 255 0 4  3 2 6 7  0 0 255 4  6 5 4 7  255 0 0
 * 1) cube.off
 * 2) A cube