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I just readed message from http://www.chaosgroup.com/news/20030206-01.html and I
wonder how many times listed limits can be multiplied and then done in POV-Ray?
Is here any V-Ray user available? Would it be possible to load the same model to
render in V-Ray and POV-Ray and compare memory usage/speed/quality ?
ABX
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ABX wrote:
>
> I just readed message from http://www.chaosgroup.com/news/20030206-01.html and I
> wonder how many times listed limits can be multiplied and then done in POV-Ray?
> Is here any V-Ray user available? Would it be possible to load the same model to
> render in V-Ray and POV-Ray and compare memory usage/speed/quality ?
That text seems to cover two quite different things:
1) rendering at large sizes without the problem of the whole render
fitting in memory - this is possible with POV-Ray from the beginning on.
2) rendering scenes with high numbers of polygons. The author of that
text seems quite enthusiastic about his ability to do so but does not
explain how his technique works. It is almost certainly a technique only
keeping a part of the polygons in RAM and having the rest on the disc.
Depending on how efficient this is handled (and how 'local' the rendered
scene is) this can be quite slow (interestingly the render speed is not
mentioned in that part...) The idea of displacement mapping and dynamic
subdivision has already been discussed in a different thread. This is not
(yet) possible with POV-Ray although as a 'compensation' it supports
direct rendering of isosurfaces which is quite unique among available
renderers.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______
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In article <3EB694E8.B3497DC9@gmx.de>,
Christoph Hormann <chr### [at] gmx de> wrote:
> The idea of displacement mapping and dynamic
> subdivision has already been discussed in a different thread. This is not
> (yet) possible with POV-Ray although as a 'compensation' it supports
> direct rendering of isosurfaces which is quite unique among available
> renderers.
POV is not entirely without these techniques: I think the bicubic patch
primitive does have an adaptive subdivision feature that can reduce
memory usage at the expense of render time. This is nowhere close to
general mesh subdivision though.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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Christopher James Huff <cja### [at] earthlinknet> wrote:
> POV is not entirely without these techniques: I think the bicubic patch
> primitive does have an adaptive subdivision feature that can reduce
> memory usage at the expense of render time. This is nowhere close to
> general mesh subdivision though.
I know next to nothing about NURBS surfaces, but as far as I understand,
they are kind of extended bicubic patches (ie. they have everything
bicubic patches have plus lots of extra control parameters to tune the
surface shape). Bicubic patches are extremely versatile, but they have
their limits, which AFAIK NURBS don't have (or at least they have less
limits).
The idea of NURBS surfaces is rather brilliant, since they have the
same advantages as bicubic patches (low memory requirements, very easy
to tesselate, but you can render them without pre-tesselation if
necessary) and I think you can represent virtually any surface with them.
I suppose that if you model your huge scene using NURBS surfaces, you
could have details equivalent to virtually hundreds of millions of triangles
without needing to actually allocate memory for all those triangles.
(Of course NURBS surfaces are easier to modify: Change one control point
and the surface around it will adapt smoothly.)
As for real triangle mesh raytracing, I think it's rather trivial to
come up with some kind of caching algorithm so that you don't need to keep
all the triangles in memory at the same time.
For instance, as POV-Ray creates an octree from the mesh, POV-Ray could
build this octree at parse time but not actually load the triangles into
memory (but eg. store them into a binary file). When triangles inside a
given octree node are needed for ray-triangle intersection test, they are
loaded into memory. A certain amount of nodes could be kept in memory,
and as new nodes are loaded, the oldest ones are freed.
This will, of course, have some impact in rendering speed, but at least
you are *able* to render meshes with thousands of millions of triangles
(and probably without it taking weeks).
(There are extreme cases where rendering this way might be even faster:
If only a minimal part of the whole mesh is needed, the unneeded parts
are never loaded into memory.)
--
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}// - Warp -
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"Warp" <war### [at] tagpovrayorg> wrote in message
news:3eb6d6b7@news.povray.org...
> I know next to nothing about NURBS surfaces, but as far as I understand,
> they are kind of extended bicubic patches (ie. they have everything
> bicubic patches have plus lots of extra control parameters to tune the
> surface shape). Bicubic patches are extremely versatile, but they have
> their limits, which AFAIK NURBS don't have (or at least they have less
> limits).
NURBS are just Non-Uniform Rational B-Splines. Basically, they ARE bicubic
patches (although the term is usually applied to a "sheet" of patches which
are connected at the seems and of which only the actual corner points, not
the control points, are manipulated).
> necessary) and I think you can represent virtually any surface with them.
Unfortunately, you cannot model every shape with a spline of any type (that
I am aware of). Just try doing a sphere, and you'll see the problem :)
> I suppose that if you model your huge scene using NURBS surfaces, you
> could have details equivalent to virtually hundreds of millions of
triangles
> without needing to actually allocate memory for all those triangles.
Unless you're up to incredibly long renders, though, POV-Ray first
tesselates them into triangles.
...Chambers
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Ben Chambers <bdc### [at] junocom> wrote:
> Unless you're up to incredibly long renders, though, POV-Ray first
> tesselates them into triangles.
I didn't know that POV-Ray supports NURBS.
--
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}// - Warp -
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"Ben Chambers" <bdc### [at] junocom> wrote in
news:3eba9f93@news.povray.org:
>
> "Warp" <war### [at] tagpovrayorg> wrote in message
> news:3eb6d6b7@news.povray.org...
>> I know next to nothing about NURBS surfaces, but as far as I
>> understand,
>> they are kind of extended bicubic patches (ie. they have everything
>> bicubic patches have plus lots of extra control parameters to tune
>> the surface shape). Bicubic patches are extremely versatile, but they
>> have their limits, which AFAIK NURBS don't have (or at least they
>> have less limits).
>
> NURBS are just Non-Uniform Rational B-Splines. Basically, they ARE
> bicubic patches (although the term is usually applied to a "sheet" of
> patches which are connected at the seems and of which only the actual
> corner points, not the control points, are manipulated).
AFAIK NURBS surface patches are not limited to being bicubic.
Their rational polynomials can be of any degree.
When you say that only the corner "points" are manipulated
when NURBS patches are stitched together, are you then
thinking of patches made with open knot vectors ?
> Unfortunately, you cannot model every shape with a spline of any type
> (that I am aware of). Just try doing a sphere, and you'll see the
> problem :)
I have an idea of how a sphere might be done with a single
NURBS patch, but I have not had time to try it yet.
Tor Olav
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In article <Xns### [at] 204213191226>,
Tor Olav Kristensen <tor_olav_kCURLYAhotmail.com> wrote:
> I have an idea of how a sphere might be done with a single
> NURBS patch, but I have not had time to try it yet.
I recall reading that it is impossible to make a perfect sphere using
NURBS. However, it is fairly trivial to make something that looks like a
perfect sphere. There's just no reason to use NURBS for something as
simple as a sphere.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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