From: Vadim Pikhovich (
Date: Wed Oct 10 2001 - 16:22:08 EEST

STL - stereolithography (or more commonly, standard) tessellation language.

tessellation: the process of converting geometry into a set of polygons and
accompanying information such as color, translucency, texture, etc.

An excerpt from an article on STL format:

3D Systems pioneered the rapid prototyping industry in 1988 ( A common interface was required, one that would allow
all CAD systems to provide input to the Stereolithography Apparatus (SLA).
In conjunction with Aries Technology 3D Systems defined the
Stereolithography Tessellation Language (STL) file format. The STL file is
now the de-facto standard for all rapid prototyping systems.The STL file is
an approximation of a three-dimensional CAD model. This approximation
"meshes" the model with triangular facets (faces) - see figure 9. In fact,
STL's are analogous to finite element models (FEM), where triangular facets
replace the rectilinear elements. It is an ASCII or binary file used in

The ASCII STL file must start with the lower case keyword solid (header)
and end with endsolid (footer). Within these keywords are listings of
individual triangles that define the faces of the solid model (body). Each
individual triangle description defines a single normal vector directed
away from the solid's surface followed by the xyz components for all three
of the vertices. These values are all in Cartesian (rectangular)
coordinates and are floating point values. The triangle values should all
be positive and contained within the building volume. The normal vector is
a unit vector of length one based at the origin. If the normals are not
included then the software will generate them using the right hand rule.

Vadim Pikhovich

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