**From:** Adrian Bowyer (*A.Bowyer@bath.ac.uk*)

**Date:** Mon Dec 05 2005 - 01:49:54 EET

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Quoting steve <sjbaker1@airmail.net>:

*> ChathamRes@aol.com wrote:
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*> > We have an application where increasing the number of triangles in an
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*> > STL file would be useful. Have you used commercially available software
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*> > to perform this type of function?
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*>
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*> Well, there are plenty of commercial 3D modelling tools with 'smooth'
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*> functions that would add more triangles - but they can't add
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*> information that wasn't already there. All they can do is to filter
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*> the information you've got - so they might round off corners that you
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*> intended to be sharp at the same time as they smooth off corners caused
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*> by not having enough triangles to start with.
*

If you wish to retain exactly the same geometric form, but to increase the

number of triangles by a factor of 4 (i.e. to double the linear resolution),

simply write a C++/Java/Python o.w.e. program that reads in an STL file and

decomposes each triangle into 4 by splitting the three edges in half and

joining those points to form an inverted triangle in the middle and three in

the corners, then write all 4 new triangles out to the new STL file.

That's the decomposition that was used by all those old 1980's programs that

generated fractal landscapes.

Of course you can run the program as many times as you want to refine the data

as much as you want (until you run out of double precision, but by then you'll

have filled your disc...).

Yours

Adrian

http://staff.bath.ac.uk/ensab

http://reprap.org

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