I'm afraid I'm asking for the impossible, but is there some way you can convert
a POV-object (CSG, blob) to a mesh? In theory I think it should be possible,
perhaps the pvengine does something like this, but I have no idea how.

Regards,

Remco de Korte

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>I'm afraid I'm asking for the impossible, but is there some
way you can convert
>a POV-object (CSG, blob) to a mesh? In theory I think it
should be possible,
>perhaps the pvengine does something like this, but I have
no idea how.


Moray has some export formats besides pov and inc, which can
be converted with 3dwin (all in the moray package) like 3ds
(for 3d Studio Max). The objects would then have to be
converted to meshes, I guess.
The only problem then is: the mesh format 3ds (or any other
of the programs that are available for conversion) uses
isn't the same as pov uses... There would have to be some
coordinates and triangles in some of the export formats,
though...

I'm gonna see for myself now (curiosity..) I'll let you know
if I find anything.

Julius

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Julius Klatte wrote:
> 
> >I'm afraid I'm asking for the impossible, but is there some
> way you can convert
> >a POV-object (CSG, blob) to a mesh? In theory I think it
> should be possible,
> >perhaps the pvengine does something like this, but I have
> no idea how.
> 
> Moray has some export formats besides pov and inc, which can
> be converted with 3dwin (all in the moray package) like 3ds
> (for 3d Studio Max). The objects would then have to be
> converted to meshes, I guess.
> The only problem then is: the mesh format 3ds (or any other
> of the programs that are available for conversion) uses
> isn't the same as pov uses... There would have to be some
> coordinates and triangles in some of the export formats,
> though...
> 
> I'm gonna see for myself now (curiosity..) I'll let you know
> if I find anything.
> 
> Julius

I have a had a swift look at Moray but never used it. The exact format is not
the problem. If it's a file with just the 3d-coords that'll be just fine.

Regards,

Remco

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Remco de Korte wrote:
> 
> I'm afraid I'm asking for the impossible, but is there some way you can convert
> a POV-object (CSG, blob) to a mesh? In theory I think it should be possible,
> perhaps the pvengine does something like this, but I have no idea how.
> 
> Regards,
> 
> Remco de Korte

To the best of my knowledge (which is considerable) there
is currently no program tht will parse a Pov-Ray scene and
output a 3d file format usable by other programs. I seem to
recall reading something in the programers group about one
being worked one but I know nothing of the specifics.

These are the files that Pov-Ray hath make. Be glad in it
and rejoice. Psalms 19:98 10, 24

Ken Tyler

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It should be possible to convert a POV csg to a mesh with Ron Parker's
Superpatch.  I am working on it right now, but you may be able to roll
your own faster.  The basic idea is to use object_bounds to put a box
around the object, then iterate around that box using trace() to pick
off points of the object, then use any suitable triangulating algo on
the point set.  If the object is complex, you may want to use additional
planes at other angles, using the bounding box to ensure that you are
far enough away.

Jerry Anning
cle### [at] dholcom

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Remco de Korte <rem### [at] xs4allnl> wrote:
: I'm afraid I'm asking for the impossible, but is there some way you can convert
: a POV-object (CSG, blob) to a mesh? In theory I think it should be possible,
: perhaps the pvengine does something like this

  It's lamentably common that people do not distinguish between how raytracing
and scanline rendering work. Since scanline rendering is much more popular
(thanx to programs like 3DStudio), many people think that _every_ rendering
program work like those, ie. that they just make a triangle mesh with each
object and scanline-render them.
  This can be clearly seen when people ask questions like "will povray
rendering speed increase if I buy a 3D-card?" or with statements like
"actually a sphere is a polygon mesh with very small phong-shaded triangles"
which I once had to correct.
  Since many people have always worked with scanline-renderers and are very
accustomed to them, they think that every renderer work the same way.

  In povray, and I think that in every raytracer, spheres are spheres, not
polygon meshes. They are true mathematical, perfect spheres. And this applies
to almost every primitive (except for primitives like bezier patch or
heightfield).
  CSG's are mathematically calculated, not approximated with polygons.

-- 
                                                           - Warp. -

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Nieminen Mika wrote:
> 
> Remco de Korte <rem### [at] xs4allnl> wrote:
> : I'm afraid I'm asking for the impossible, but is there some way you can convert
> : a POV-object (CSG, blob) to a mesh? In theory I think it should be possible,
> : perhaps the pvengine does something like this
> 
>   It's lamentably common that people do not distinguish between how raytracing
> and scanline rendering work. Since scanline rendering is much more popular
> (thanx to programs like 3DStudio), many people think that _every_ rendering
> program work like those, ie. that they just make a triangle mesh with each
> object and scanline-render them.
>   This can be clearly seen when people ask questions like "will povray
> rendering speed increase if I buy a 3D-card?" or with statements like
> "actually a sphere is a polygon mesh with very small phong-shaded triangles"
> which I once had to correct.
>   Since many people have always worked with scanline-renderers and are very
> accustomed to them, they think that every renderer work the same way.
> 
>   In povray, and I think that in every raytracer, spheres are spheres, not
> polygon meshes. They are true mathematical, perfect spheres. And this applies
> to almost every primitive (except for primitives like bezier patch or
> heightfield).
>   CSG's are mathematically calculated, not approximated with polygons.
> 
> --
>                                                            - Warp. -

So, what do you want to say by this? How does this answer my question?
I've never used any of your 'scanline-renderers', I'm just trying to figure out
some things. I have a POV-model consisting of some spheres and blobs and all and
I want to do some warping or morphing on this. For that I'd like to have it in a
mesh-form, because they are easy to morph. 
I think you're making some unjustified assumptions.

Remco

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This is a good idea, but it will probably not work perfectly, because of
multiple intersections with trace (how do you ensure that you'll get all
of them?).  Also, you will run into problems with sharp edges getting
rounded because a sample ray doesn't hit them directly.

I know that Polyray (another very good ray-tracer) has the ability to
convert primatives into wireframe (in fact, it also does scan-line
rendering).  I think that this would be a very good thing to add to
POV-Ray, since it would facilitate non-linear transformations (among
other things).

-Nathan Kopp

Jerry Anning wrote:
> 
> It should be possible to convert a POV csg to a mesh with Ron Parker's
> Superpatch.  I am working on it right now, but you may be able to roll
> your own faster.  The basic idea is to use object_bounds to put a box
> around the object, then iterate around that box using trace() to pick
> off points of the object, then use any suitable triangulating algo on
> the point set.  If the object is complex, you may want to use additional
> planes at other angles, using the bounding box to ensure that you are
> far enough away.
> 
> Jerry Anning
> cle### [at] dholcom

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On Sun, 25 Oct 1998 00:09:36 -0400, Nathan Kopp <Nat### [at] Koppcom>
wrote:

>This is a good idea, but it will probably not work perfectly, because of
>multiple intersections with trace (how do you ensure that you'll get all
>of them?).  Also, you will run into problems with sharp edges getting
>rounded because a sample ray doesn't hit them directly.

I guess you trace again after you find the first intersection,
starting just past the first intersection.  But I'd rather watch my
grass grow than actually do such a thing.  There's also the issue of
how you determine which points are on the same surface once you've
found your cloud of intersection points.  And, of course, the limits
to any sampling scheme: the rounded edges you mention, plus aliasing.

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Nieminen Mika wrote:

/.../
>   Since many people have always worked with scanline-renderers and are very
> accustomed to them, they think that every renderer work the same way.
> 
>   In povray, and I think that in every raytracer, spheres are spheres, not
> polygon meshes. They are true mathematical, perfect spheres. And this applies
> to almost every primitive (except for primitives like bezier patch or
> heightfield).
>   CSG's are mathematically calculated, not approximated with polygons.
> 
> --
>                                                            - Warp. -

Correct me if I'm wrong, but is the fact that most POV primitives are
mathematical and 'perfect', an advantage - and yet a weakness?
As far as I know, things like non-linear transformations and true
displacement mapping require objects to be converted to triangles. These
things cannot be done in POV (except height_fields, which are true
displacements and consist of triangles).
I know that BMRT, a very good Renderman-compliant raytracer, can do true 
displacement mapping on objects - therefore albeit it is a raytracer, it
probably _does_  convert primitives into triangles for this purpose.

Margus

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