The file simply ends after the last triangle.Įach triangle is described by twelve 32-bit floating-point numbers: three for the normal and then three for the X/Y/Z coordinate of each vertex – just as with the ASCII version of STL. Following that is data describing each triangle in turn. Following the header is a 4-byte little-endian unsigned integer indicating the number of triangular facets in the file. A binary STL file has an 80-character header (which is generally ignored, but should never begin with 'solid' because that may lead some software to assume that this is an ASCII STL file). Binary STL īecause ASCII STL files can be very large, a binary version of STL exists. The spaces between 'facet' and 'normal' and between 'outer' and 'loop' are required. White space (spaces, tabs, newlines) may be used anywhere in the file except within numbers or words.

In practice, however, all facets are simple triangles. The structure of the format suggests that other possibilities exist (e.g., facets with more than one 'loop', or loops with more than three vertices). STL files contain no scale information, and the units are arbitrary. In the original specification, all STL coordinates were required to be positive numbers, but this restriction is no longer enforced and negative coordinates are commonly encountered in STL files today. Īn STL file describes a raw, unstructured triangulated surface by the unit normal and vertices (ordered by the right-hand rule) of the triangles using a three-dimensional Cartesian coordinate system. Binary files are more common, since they are more compact. The STL format specifies both ASCII and binary representations.

STL files describe only the surface geometry of a three-dimensional object without any representation of color, texture or other common CAD model attributes. This file format is supported by many other software packages it is widely used for rapid prototyping, 3D printing and computer-aided manufacturing. STL has several backronyms such as 'Standard Triangle Language' and 'Standard Tessellation Language'. STL is a file format native to the stereolithography CAD software created by 3D Systems.

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