This blog is mainly to help you understand better the procees of 3d printing. Since all 3d file formats are conveyable into STL format lets try and unserstand what is an STL file.

STL is a file format native to the stereolithography CAD software created by 3D Systems. This file format is supported by many other software packages; it is widely used for rapid prototyping and computer-aided manufacturing. STL files describe only the surface geometry of a three dimensional object without any representation of color, texture or other common CAD model attributes. The STL format specifies both ASCII and binary representations. Binary files are more common, since they are more compact. An 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.

History of use
Stereolithography machines are basically 3D printers that can build any volume shape as a series of slices. Ultimately these machines require a series of closed 2D contours that are filled in with solidified material as the layers are fused together.

The natural file format for such a machine would be a series of closed polygons corresponding to different Z-values. However, since it's possible to vary the layer thicknesses for a faster though less precise build, it seemed easier to define the model to be built as a closed polyhedron that could be sliced at the necessary horizontal levels.

The STL file format appears capable of defining a polyhedron with any polygonal facet, but in practice it's only ever used for triangles, which means that much of the syntax of the file is superfluous. It is also the case that the value of the normal shouldn't be necessary, since that is a direct calculation from the coordinates of the triangle with the orientation being controlled by the right hand rule.

STL files are supposed to be closed and connected like a combinatorial surface, where every triangular edge is part of exactly two triangles, and not self-intersecting.

However, for the purpose of generating a single contour slice using a very lightweight piece of software on a computer with little memory, this format is perfect since it can be processed in one pass regardless of file size.

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