According to the drawing or design intent, the CAD entity file of the part is designed in the 3D CAD design software. The file output format supported by general rapid prototyping is the STL model, that is, the so-called surface treatment for approximating the solid surface, which is to approximate the model surface with a planar triangular patch. To simplify the data format of the CAD model, to facilitate subsequent layered processing.
Because it is relatively simple in data processing and independent of the CAD system, it quickly developed into a standard for data exchange between CAD systems and rapid prototyping machines in the field of rapid prototyping. Each triangular patch is represented by four data items. That is, three vertex coordinates and one normal vector, the entire CAD model is such a collection of vectors. In the general software system, the output precision control parameters can be adjusted to reduce the surface approximation processing error. For example, the Pre 1E software uses the ch-chordheight as the accuracy parameter for approximation.