Craig Gotsman wrote:
> Do the triangles have to be sorted in any specific way inside
> the STL file in order to be a legitimate input to an RP machine ?
>
> In other words, is this statement (from a colleague of mine) correct:
> "If the points are out of order (or not bottom-top in fact), any Stereo
> Lithography machine will construct the model improperly, if at all. As
> most of these types of machines work with the STL format, they build
> the physical model up a single layer at a time. If the layers aren't
> properly sorted, all manner of problems can arise."
Craig,
It is certainly true that the layers have to be correctly sorted in a
slice file, but sorting of triangles in an StL file is not necessarily
possible, let alone required, and there is no provision in the StL
specification for sorting of triangles.
Within each layer of a slice file, different fabricators will have
different data requrements. An Actua, which is a purely raster device, will
use its layer data differently than a purely vector machine, such as an LOM.
An SLA or FDM, which combines both vector (for edges) and raster (for
interiors), will be different again.
For vector processing, what is necessary is that the line segments, which
are the cross sections of the triangles with the layer, are ordered and
oriented, so that they form a set of closed polygons. In addition, it helps
if the construction and sequence of polygons is optimized in such a way as to
reduce processing time.
I hope these comments are of some help to you.
Best regards,
Marshall Burns
Marshall@Ennex.com
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