POV-Ray : Newsgroups : povray.general : Anybody know this site? Server Time
9 Aug 2024 15:21:37 EDT (-0400)
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From: 25ct
Subject: Re: Anybody know this site?
Date: 13 Aug 2000 10:06:44
Message: <3996ab74$1@news.povray.org>
"Alan Kong" <ako### [at] povrayNO-SPAMorg> wrote in message
news:9j9dpskbadaq99b7j75a7ilngf83t6f3e0@4ax.com...
> On Sun, 13 Aug 2000 10:01:47 +0100 "25ct" <25c### [at] lineonenet> wrote:
>
> >   After rendering, do the images save as .bmp's by default? And is it ok
to
> >send to pov.images in this format?


>
>   Hi, Steve. I suggest reading all of the messages in the
> povray.announce.frequently-asked-questions group, specifically "Where
> can I post my binary or text file?"


>
> --
> Alan - ako### [at] povrayorg - a k o n g <at> p o v r a y <dot> o r g
> http://www.povray.org - Home of the Persistence of Vision Ray Tracer

       Thanks Alan. I have subscribed to it, but haven't got around to
reading the messages yet. Been busy with an image! (ref; pov.images)  ;o)
It's next on my list though.

                 ~Steve~


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From: Chris Huff
Subject: Re: Anybody know this site?
Date: 13 Aug 2000 12:00:25
Message: <chrishuff-55C3C2.11013413082000@news.povray.org>
In article <3996558A.CDAA55FF@kivisalo.net>, Kari Kivisalo 
<kar### [at] kivisalonet> wrote:

> I think the equations  would just be
> 
> u(xx) + u(yy) + u(zz) = 0 and
> 
> u(x+1,y,z) + u(x,y+1,z) + u(x-1,y,z) + u(x,y-1,z) + u(x,y,z+1) + 
> u(x,y,z-1) = 6*u(x,y,z)

Yeah, but the problem is figuring out what that means. :-)
It looks simple, but I can't translate it into an algorithm, and I have 
only a slight idea what u() is supposed to do.


> I could convert my code quite easy to 3D for testing purposes but it 
> would require lots of RAM to run. Then I would write a macro that 
> outputs an object/volume as voxel image slice by slice as animation. 
> What's the format of the pov voxel image type (for input to pov)?

Does it require that the density field be converted to a voxel image? I 
hope not...but if it requires multiple passes that can't be done at 
once, I don't see a way around it.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/


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From: Kari Kivisalo
Subject: Re: Anybody know this site?
Date: 13 Aug 2000 12:50:39
Message: <3996D1F6.24D7B16@kivisalo.net>
Chris Huff wrote:
> > u(xx) + u(yy) + u(zz) = 0 and
> >
> > u(x+1,y,z) + u(x,y+1,z) + u(x-1,y,z) + u(x,y-1,z) + u(x,y,z+1) +
> > u(x,y,z-1) = 6*u(x,y,z)
>
> only a slight idea what u() is supposed to do.

u is the density/potential at (x,y,z).

> Does it require that the density field be converted to a voxel image? 

As I said before this algrithm is a numerical discrete approximation,
not analythical. The input and output are are voxel images just like
the 2d case works with 2d images. Only certain special cases of potential
fields can be solved analythically at any point. The whole volume must
be solved at once so it's impossible solve just one point at a time.

In povray terms this requires a pre-rendering pass to sample the volume
of interest at specified resolution and then solving the potential field
within that volume.

K.K.


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From: Chris Huff
Subject: Re: Anybody know this site?
Date: 13 Aug 2000 14:01:29
Message: <chrishuff-BAD5A3.13023513082000@news.povray.org>
In article <399### [at] kivisalonet>, Kari Kivisalo 
<kar### [at] kivisalonet> wrote:

> u is the density/potential at (x,y,z).

Simply the field value? Then this is nothing more than a kind of 3D 
convolution matrix...right? Basically a blurring operation.


> > Does it require that the density field be converted to a voxel image? 
> 
> As I said before this algrithm is a numerical discrete approximation,
> not analythical. The input and output are are voxel images just like
> the 2d case works with 2d images. Only certain special cases of potential
> fields can be solved analythically at any point. The whole volume must
> be solved at once so it's impossible solve just one point at a time.

Are you sure about this? It seems like some kind of recursive algorithm 
could be used to do a similar effect, sampling at one distance, 
subdividing and interpolating, sampling again, etc. I am going to have 
to experiment with this...
It wouldn't be the same algorithm, but it should be similar in results.


> In povray terms this requires a pre-rendering pass to sample the volume
> of interest at specified resolution and then solving the potential field
> within that volume.

This could most easily be done in the parsing stage, and would probably 
be a density_file pattern internally. However, you would have to specify 
a resolution large enough, and it would consume a lot of memory. :-(
If this absolutely requires a voxel image, then might as well implement 
it as a density_file feature, and add the ability to create a 
density_file pattern from another pattern(like object). You could 
already do so with a macro and eval_pattern() or eval_pigment(), but the 
parse time would be long.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/


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From: Kari Kivisalo
Subject: Re: Anybody know this site?
Date: 13 Aug 2000 16:40:40
Message: <399707DB.C0075861@kivisalo.net>
Chris Huff wrote:
>
> > u is the density/potential at (x,y,z).
> 
> Simply the field value? Then this is nothing more than a kind of 3D
> convolution matrix...right? Basically a blurring operation.

One iteration of the linear system is just a blur which can be seen
from the bevel mode example pictures. When the change between iterations
drops below tolerance that's the solution for the Laplace equation.

> > The whole volume must
> > be solved at once so it's impossible solve just one point at a time.
> 
> Are you sure about this?

That math book I mentioned only spoke about methods using linear systems
of equations and iteration. There may be other numerical methods geared
towards applications other than electrical engineering. Look for them using
laplace, poisson , differential, numerical.



K.K.


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