BYU Geometry File Format

The file format was invented by Brigham Young University for geometric surface shapes in 3D space. It is a very classic format specified in the 70s but still used in CAD systems.

These files use fixed format, i.e. fixed length for all variables.

The meaning of the variables is as follows:

First line of the file:

nparts npoints npolys nconnects ntest

nparts

number of parts of a geometry, each is a separate surface in the same file

npoints

total number of coordinate vectors in Rū

npolys

number of patches, (a triangle, a quadrilateral are all single patches e.g.)

nconnects

number of connectivity entries (that is for triangles only: 3 * npolys)

ntest

should be 0

Next lines specify boundaries of the parts, i.e. the position of the first and
last entry of the part in the connectivity list of the file

first1 last1
first2 last2
...

Next lines specify the coordinate vectors in Rū off all coordinates:
Each row has six numbers (that is two points) each one with twelve digits
(like shown below) inclusive blanks and right-aligned.

Next lines specify the indices of the coordinates in the coordinate vector
that make up a patch, and this for each patch of the whole surface.
Here every line must have 16 entries with each one six digits (also inclusive
blanks and right-aligned). The last connectivity entry
of such a patch has negative sign to indicate the end of the patch.
This allows patches of arbitrary number of edges, but it's better to use triangles,
otherwise an automatic triangulation algorithm would be invoked.

An example file is given below (it is a cube):