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A STL file is a triangular representation of a 3D object. The surface of an object is
broken into a logical series of triangles (see illustration at right). Each triangle is
uniquely defined by its normal and three points representing its vertices.
The file begins with a solid record, (which can include a name for the object), and
ends with an endsolid record. Each triangle begins with a facet record and ends with
an endfacet record. The normal vector, if given, is included as part of the facet
record, and is identified by the normal keyword. The normal vector should have unit
length. The three vertices of the triangle are delimited by outer loop and endloop
records. Each vertex is described on a vertex record that lists its (X,Y,Z) coordinates.
An ASCII STL file for a four-face figure that's a slice of a cube would be:
solid cube_corner
facet normal 0.0 -1.0 0.0
outer loop
vertex 0.0 0.0 0.0
vertex 1.0 0.0 0.0
vertex 0.0 0.0 1.0
endloop
endfacet
facet normal 0.0 0.0 -1.0
outer loop
vertex 0.0 0.0 0.0
vertex 0.0 1.0 0.0
vertex 1.0 0.0 0.0
endloop
endfacet
facet normal 0.0 0.0 -1.0
outer loop
vertex 0.0 0.0 0.0
vertex 0.0 0.0 1.0
vertex 0.0 1.0 0.0
endloop
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