Since the STL syntax does not enforce this property, it can be ignored for applications where the void does not matter.The STL format specifies both ASCII and binary representations.Binary files are more common, since they are more compact.
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. STL files contain no scale information, and the units are arbitrary. The file continues with any number of triangles, each represented as follows. The spaces between facet and normal and between outer and loop are required. 3D Software Stl File Format Software To AssumeA 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). Following the header is a 4-byte little-endian unsigned integer indicating the number of triangular facets in the file. If color is used, then somewhere in the header should be the ASCII string COLOR followed by four bytes representing red, green, blue and alpha channel (transparency) in the range 0255. This is the color of the entire object, unless overridden at each facet. Magics also recognizes a material description; a more detailed surface characteristic. Just after COLORRGBA specification should be another ASCII string,MATERIAL followed by three colors (34 bytes): first is a color of diffuse reflection, second is a color of specular highlight, and third is an ambient light. The per-facet color is represented in the two attribute byte count bytes as follows. There is also no way to have facets be selectively transparent because there is no per-facet alpha value although in the context of current rapid prototyping machinery, this is not important. Some STL loaders (e.g. STL plugin for Art of Illusion) check that the normal in the file agrees with the normal they calculate using the right-hand rule and warn the user when it does not. Other software may ignore the facet normal entirely and use only the right-hand rule. Although it is rare to specify a normal that cannot be calculated using the right-hand rule, in order to be entirely portable, a file should both provide the facet normal and order the vertices appropriately. This requires a series of closed 2D contours(horizontal layers) that are filled in with solidified material as the layers are fused together. A natural file format for such a machine would be a series of closed polygons (layers or slices) corresponding to different Z-values. However, since it is possible to vary the layer thicknesses for a faster though less precise build, it was easier to define the model to be built as a closed polyhedron that can be sliced at the necessary horizontal levels. An incorrect facet normal can affect the way a file is sliced and filled. A slice at a different Z-value can be chosen to miss a bad facet or the file must be returned to CAD program to make corrections and then regenerate the STL file.
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