The Facet Normal
In both ASCII and binary versions of STL, the facet normal should be a unit vector pointing outwards from the solid object. In most software this may be set to (0,0,0) and the software will automatically calculate a normal based on the order of the triangle vertices using the 'right-hand rule'. Some STL loaders (e.g. the 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 you 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. A notable exception is SolidWorks which uses the normal for shading effects.
Read more about this topic: STL (file Format)
Famous quotes containing the words facet and/or normal:
“Humankind has understood history as a series of battles because, to this day, it regards conflict as the central facet of life.”
—Anton Pavlovich Chekhov (1860–1904)
“Cant is always rather nauseating; but before we condemn political hypocrisy, let us remember that it is the tribute paid by men of leather to men of God, and that the acting of the part of someone better than oneself may actually commit one to a course of behaviour perceptibly less evil than what would be normal and natural in an avowed cynic.”
—Aldous Huxley (1894–1963)