OFF (file format)

OFF (Object File Format) is a geometry definition file format containing the description of the composing polygons of a geometric object.[1] It can store 2D or 3D objects, and simple extensions allow it to represent higher-dimensional objects as well.[2] Though originally developed for Geomview, a geometry visualization software, other software has adapted the simple standard.[3]

OFF geometry format
Filename extension
.off
Internet media type
text/plain
Type of format3D model format

Composition

The composition of a standard OFF file is as follows:[4]

  • 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:[5]

  • 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
# cube.off
# A cube
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

See also

References
  1. "OFF file format (Princeton)".
  2. Burkardt, John. "Geomview Object File Format".
  3. Holmes, Ryan. "OFF Files".
  4. Holmes, Ryan. "OFF Files".
  5. Webb, Robert (2020). "Stella4D Pro Manual".
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