The ASCII format, on the other hand, has the advantage of being easy to understand and read even by an operator, which is useful only if you want to manually change the coordinates or information relating to the individual triangles. The binary type file is the most convenient and used due to the best efficiency in terms of space occupied (it can reach a quarter of the corresponding file in ASCII format) and is recommended for applications related to additive manufacturing. These are just two different ways of saving and formatting information about the triangle mesh.

The STL format has two different saving standards: ASCII and binary. In this article we are going to analyze these problems. This leads to a series of problems, as we can see from the image shown here as an example, dictated to approximate curved contours with broken straight lines. The STL file in fact saves, for each triangle, only the coordinates of the 3 vertices in space (coordinates x, y, z) and the direction of the normal. It is important to underline that the STL format, unlike the CAD formats such as the step, is 'ignorant' of how the object was modeled and constructed or how the surfaces that form it are mathematically defined. The information of where the inside of the component is located is saved in every single triangle by defining the normal, a line coming out of the triangle and perpendicular to it.

Unlike other CAD formats, the object appears to be formed only by the external surface or 'skin'. 3D geometry is described by a mesh of triangles and dimensional information is contained in each individual triangle.

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