I would like to build it from small parts like triangles and I know

about a number of points randomly scattered over the surface and then
make triangles with those.

TIA

Remco de Korte

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Remco de Korte wrote:


> I would like to build it from small parts like triangles and I know

> about a number of points randomly scattered over the surface and then
> make triangles with those.
>
> TIA
>
> Remco de Korte

    In a way isn't that what lathes, sors, and prisms do ?

    If that's not a satisfactory approach there is a great little
Dos utility called Geodome that creates shapes of the same
name.
    It offers some user options that allow you to control
the number of nodes, spherical or cylindrical shape, and
direction scaling.
    It's output spits out triangles and optionally cylinders, acting
as cross supports, and Pov spheres as node connection points.
    Geodome might do what you want. If not the triangles are
there and can be moved or removed as needed to get the shape
you want
    If you can't located geodome I think it's on the POV-Ray
ftp server. If not it's a small program which I have on CD
so I could send you a copy.

    I took the time once to hand code a sphere like object with
triangles and I definitely don't recommend others try this.

Ken

Post a reply to this message

Ken wrote:
> 
> Remco de Korte wrote:
> 


> > I would like to build it from small parts like triangles and I know

> thinking
> > about a number of points randomly scattered over the surface and
> then
> > make triangles with those.
> >
> > TIA
> >
> > Remco de Korte
> 
>     In a way isn't that what lathes, sors, and prisms do ?
> 
>     If that's not a satisfactory approach there is a great little
> Dos utility called Geodome that creates shapes of the same
> name.
>     It offers some user options that allow you to control
> the number of nodes, spherical or cylindrical shape, and
> direction scaling.
>     It's output spits out triangles and optionally cylinders, acting
> as cross supports, and Pov spheres as node connection points.
>     Geodome might do what you want. If not the triangles are
> there and can be moved or removed as needed to get the shape
> you want
>     If you can't located geodome I think it's on the POV-Ray
> ftp server. If not it's a small program which I have on CD
> so I could send you a copy.
> 
>     I took the time once to hand code a sphere like object with
> triangles and I definitely don't recommend others try this.
> 
> Ken

Thanks, I'll try that.

Regards,

Remco

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Remco de Korte wrote:
> 

> I would like to build it from small parts like triangles and I know

> about a number of points randomly scattered over the surface and then
> make triangles with those.

You could use my rock making .INC file.  It's at

http://www.erols.com/vansickl/rock.htm

Regards,
John

Post a reply to this message

> Remco de Korte wrote:
> >

> > I would like to build it from small parts like triangles and I know

> > about a number of points randomly scattered over the surface and then
> > make triangles with those.

There are numerous ways to do "spheres" with lots of polygons.The best I can
see is to use a "Buckminster-Fuller"-type polyedron.
You start with an icosaedron (20 faces... you know, d&d 20 sided
dice) then progressively divide the faces into 4 other triangles. You
keep dividing triangles until you've got a satisfying result.

IMHO, there's no real use to that. A sphere is much better repre-
sented when it's a z^2+y^2+X^2=r^2 form; especially if your
only goal is to render a simple sphere.

On the other hand, the buckminsterized sphere provide almost
uniform sampling points on the sphere; you dont have the point
concentration effect you have with polar/spheric coordinates. It
is also ideal for spheric fractals (or "rocks", either John's generator,
http://www.erols.com/vansickl/rock.htm, or my own generator,
http://www.iro.umontreal.ca/~pigeon/pub/PovPage/RockGen/RockGen.html
(with source included)).

I first buckminsterized spheres to do uniform sampling, in the
context of environment mapping (to reduce rendering time).
Then for to fractal planets.


Best,

    S.
 ----------------------------------------------------------
Steven Pigeon                     Ph. D. Student.
University of Montreal.
pig### [at] iroumontrealca           Topics: data compression,
pig### [at] jspumontrealca          signal processing,
ste### [at] researchattcom           non stationnary signals
                                  and wavelets.
----------------------------------------------------------
         http://www.iro.umontreal.ca/~pigeon

Post a reply to this message

Steven Pigeon wrote:
> 
> > Remco de Korte wrote:
> > >


> > > I would like to build it from small parts like triangles and I
> know

> thinking
> > > about a number of points randomly scattered over the surface and
> then
> > > make triangles with those.
> 
> There are numerous ways to do "spheres" with lots of polygons.The best
> I can
> see is to use a "Buckminster-Fuller"-type polyedron.
> You start with an icosaedron (20 faces... you know, d&d 20 sided
> dice) then progressively divide the faces into 4 other triangles. You
> keep dividing triangles until you've got a satisfying result.
> 
> IMHO, there's no real use to that. A sphere is much better repre-
> sented when it's a z^2+y^2+X^2=r^2 form; especially if your
> only goal is to render a simple sphere.
> 
> On the other hand, the buckminsterized sphere provide almost
> uniform sampling points on the sphere; you dont have the point
> concentration effect you have with polar/spheric coordinates. It
> is also ideal for spheric fractals (or "rocks", either John's
> generator,
> http://www.erols.com/vansickl/rock.htm, or my own generator,
> http://www.iro.umontreal.ca/~pigeon/pub/PovPage/RockGen/RockGen.html
> (with source included)).
> 
> I first buckminsterized spheres to do uniform sampling, in the
> context of environment mapping (to reduce rendering time).
> Then for to fractal planets.
> 
> Best,
> 
>     S.
>  ----------------------------------------------------------
> Steven Pigeon                     Ph. D. Student.
> University of Montreal.
> pig### [at] iroumontrealca           Topics: data compression,
> pig### [at] jspumontrealca          signal processing,
> ste### [at] researchattcom           non stationnary signals
>                                   and wavelets.
> ----------------------------------------------------------
>          http://www.iro.umontreal.ca/~pigeon

I downloaded the program Ken mentioned (Geodome1). There's a really nice
image by the same name at the FTP-site.
I had a look at the program and though it does do what it's supposed to
do it wasn't exactly what I needed (my question was a bit vague). I had
a look at the source though and that brought me to the idea to do
something like you describe here: a recursive function, creating a
sphere with triangles, subdivided by triangles, etc. With this I could
do what I actually intended to: to blow up a sphere into fragments.

You're right that it wouldn't be very smart to use this method if you'd
just need a sphere. Even with smooth-triangles I found that there were
seams all over the object. But if you'd need any 'special effects' (
abump in a sphere) you could consider this (or use a blob).

Regards,

Remco de Korte
http://www.xs4all.nl/~remcodek

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> do what I actually intended to: to blow up a sphere into fragments.

For this application, also consider :

http://www.geocities.com/SiliconValley/Lakes/1434/explode.html

a generalized explosion macro by the incredible Chris Colfax
(who accomplishes with include files things for which normal folk
must hack the source....)

Dan

-- 
http://www.flash.net/~djconnel/

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Dan Connelly wrote:

> For this application, also consider :
> http://www.geocities.com/SiliconValley/Lakes/1434/explode.html
> a generalized explosion macro by the incredible Chris Colfax
> (who accomplishes with include files things for which normal folk
> must hack the source....)
>
> Dan

Can people who sit around designing computer graphic images
using POV-Ray be concidered normal folk ?

Ken

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Ken wrote:

> > (who accomplishes with include files things for which normal folk
> > must hack the source....)
> >
> > Dan
>
> Can people who sit around designing computer graphic images
> using POV-Ray be concidered normal folk ?
>
> Ken

No, of course not :-) Especially those who have their own
builds and home-made companion programs ...!


Best,

    S.


----------------------------------------------------------
Steven Pigeon                     Ph. D. Student.
University of Montreal.
pig### [at] iroumontrealca           Topics: data compression,
pig### [at] jspumontrealca          signal processing,
ste### [at] researchattcom           non stationnary signals
                                  and wavelets.
----------------------------------------------------------
         http://www.iro.umontreal.ca/~pigeon

Post a reply to this message

Ken wrote in message <35FBC490.FCEDA158@pacbell.net>...
>Can people who sit around designing computer graphic images

>using POV-Ray be concidered normal folk ?

>

>Ken

>


I hear this question, but more specifically asked than here, about a dozen times every
day. My mother, my father, my brother, all my friends, my girlfriend... Now I hear it
from a fellow POVer. They can't be all wrong, you know. I guess I'll have to admit I'm
"kinda nuts".

Peter

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