On Fri, 1 Mar 1996, Gary Scholl wrote:
> In a solid model, a planar facet defines a boundary. The normal in the STL
> format is only utilized to differentiate between the side with mass and the
> side without mass. (A more compact approach would have been to have specify
> the sequence of listing the three vertices so as to remove the ambiguity of
> the normal)
The StL specification does specify the order of listing the
vertices, according to the "right-hand rule" (counterclockwise when
looking at the facet from outside the object). The normal data is
completely redundant. The thinking behind including the normal data was
probably to give the burden of computation to the program generating the
StL code, and reduce the computation needed in the slicing program.
Best regards,
Marshall Burns
marshall@ennex.com
*************************************************************************
** Ennex(TM) Fabrication Technologies **
** Your source for expertise on automated fabrication(TM) **
******* *******
** 10911 Weyburn Avenue, Suite 332, Los Angeles, U.S.A. 90024 **
** Phone: +1 (310) 824-8700 Fax: +1 (310) 824-5185 **
** E-Mail: autofab@ennex.com **
*************************************************************************
This archive was generated by hypermail 2.1.2 : Tue Jun 05 2001 - 22:37:13 EEST