I dont think there is a need for the triangles to be ordered in the STL file.
According to my knowledge, the simplest slicing routine works with a slicing
plane that "steps through" the 3D part in increments (equal to teh slice
thk.), scans all the triangles looking for any intersections with it. All the
intersections are recorded for each slicing plane (at a particular z height),
and individual line segments from the intersections are later joined together
to form the contours of a layer.
I am sure the SFF manufacturers use faster algorithms in their
processing software (probably use a topological data structure with
triangle-triangle adjacency info, in which case too there is no need for the
triangles to be ordered), but I am pretty sure the order of the triangles
doesnt matter.
gautham
------------------------------------------------------------------------
Gautham Kattethota Home : 950, South Terrace Road, #C349
Grad. student, Tempe AZ 85281
Dept. of MAE,Mail Code: 6106 Res Ph# : (602)967-4362
Arizona State University, Off Ph# : (602)965-7830
Tempe, AZ 85287 Email : gautham@asu.edu
------------------------------------------------------------------------
On Sun, 22 Nov 1998 kevan_jones@cemcom.com wrote:
> Speaking with regard to 3D systems SLA machine, it seems to me that the
> (numerical?) order of the triangles in the .stl file is not as important as
> their location and normal orientation wrt the origin. The SLA machine does
> not work with the .stl file. It uses the Build Format File (.bff) which
> contains the layer information. Obviously, if these layers are out of
> order, then the SLA machine is going to build something rather strange (if
> it builds at all). The software which creates the .bff file needs to know
> the location and normal orientation of the triangles in the .stl file, but
> I don't see how an order might be important. If anyone has any other
> thoughts, please step in, as I do not claim to be an expert on the
> technical issues regarding how the zslice routines work, or use the .stl
> file.
>
> Kevan Jones
> Director, Information Systems
> CEMCOM Corporation
> 4100 Pistorio Rd
> Baltimore, MD 21229
> www.cemcom.com
>
>
>
> For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>
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