On 18/09/2025 15:09, Kenneth wrote:
> 
> This entire discussion interests me greatly! And it finally shook me out of my
> lazy doldrums. (Real-life took over this summer-- work, plumbing problems, and
> more dental problems.) Anyway...
> 
> Having ascii-STL-to-mesh (or mesh2) conversion built-in 'under-the-hood' would
> be a great addition to POV-ray. But since v4.0 is still a long way off(?), some
> kind of STL-to-POV-ray-SDL conversion script would be *most* welcome.
> 
> Kurtz's ascii-STL-to-mesh conversion-- vial a Perl script-- is an amazingly
> successful piece of code, and very elegant. The excellent mesh result speaks for
> itself. I don't know Perl, but I am *almost* convinced that a similar piece of
> code could be written directly in POV's SDL, using #read and #write, because the
> syntax used in typical STL files is so simple. The conversion code would
> probably not be as elegant as Kurtz's, but that's a small price to pay.
> 
> Speaking of simplicity, I would argue that converting to a mesh (rather than
> mesh2) would be the way to go-- as in Kurtz's result.  It's much simpler to
> implement, AND much simpler to edit afterwards, should the need arise. The mesh2
> format and syntax is more 'abstract', and the docs' example of how it works (and
> how to write it successfully) is lacking...although the necessary understanding
> can be teased-out (with help from Wikipedia :-) -- at  "triangle mesh", under
> 'index arrays'.) But I think that a simpler 'mesh' construct would be easier to
> create from an STL file,  when using #read/#write.
> 
> Mention was made here of possibly adding 'normals' to the resulting mesh
> conversion-- which I take to mean, converting the triangles to 'smooth
> triangles', so that curvy surfaces appear smooth in the POV-ray render, rather
> than as the original STL flat-triangle 'facets'. But that may not produce the
> intended effect for an *entire* model, as there could be smooth areas as well as
> sharp angles and corners. Kurtz's "att.low.jpeg" example image shows such a
> model. (The visual smoothing effect would depend on the triangle resolution, of
> course.) The problem is that, in an STL file, there is no way to know which
> triangles should be 'smoothed' and which should not; they are all just flat
> facets.
> 
> An alternate scheme would be to slightly alter the vertex positions of all of
> the flat triangles, to produce a somewhat similar smoothing effect in the POV
> render...although I have no idea as to how that is accomplished, algorithm-wise.
> ------------
> Kurtz's posted file package here has the original STL 'crate' model from
> Thingaverse. That model actually has a few minor triangle (or normal?) flaws,
> when seen in Meshmixer (and when 3-D-printed via CURA software; I printed a
> small section of the crate, just to see.) I have noticed this in other
> Thingaverse files as well. Apparently, no check is made of uploaded models
> there, to make sure that the models are 'robust' and completely correct.
> 



Thanks Kenneth.


I completely agree with your message and I would just like to add these 
few points :

* Bad STL source, bad mesh.
* Adding 3D formats directly to POVRay is definitely a good thing, but 
then for STL and not OBJ and not 3DS,...
* I understand, but I may be mistaken, that William F Pokorny is working 
alone to improve and develop version 4 of POV, and that this is already 
an enormous task.
* Adding support for other file formats would require even more work. Of 
course, we could consider creating specific plugins for each format, but 
POV's architecture does not allow for this. This is not a criticism, but 
in 1986 the concept of add-ons did not exist.




Regards,


-- 
kurtz le pirate
compagnie de la banquise

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