Here's the image illustrating my problem from povray.general.  In case
you didn't see that one, I'm looking for a macro that eliminates the
need to enter the red points manually in the bezier patch.  Thanks.

 - Rico

Post a reply to this message

Attachments:
Download 'bp2.jpg' (14 KB)

Preview of image 'bp2.jpg'

Reusser wrote:
> 
> Here's the image illustrating my problem from povray.general.  In case
> you didn't see that one, I'm looking for a macro that eliminates the
> need to enter the red points manually in the bezier patch.  Thanks.
> 

Why don't you just use a blob with two cylinder components?

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

Post a reply to this message

Christoph Hormann wrote:

> Why don't you just use a blob with two cylinder components?
>
> Christoph

I tried many things such as blobs, cylinders, and meshes, but the joints
got very ugly with blobs where there were three or four intersecting
cylinders all starting from slightly different places.  If you look by the
pedals on a bike, there are about five tubes that all affect each other but
start from different spots.  There are also a couple of bent tubes on a
bike such as the fork and the spot in the back where the down tubes
diverge.  Those aren't possible with blobs.

 - Rico

Post a reply to this message

Reusser wrote:
> 
> I tried many things such as blobs, cylinders, and meshes, but the joints
> got very ugly with blobs where there were three or four intersecting
> cylinders all starting from slightly different places.  If you look by the
> pedals on a bike, there are about five tubes that all affect each other but
> start from different spots.  There are also a couple of bent tubes on a
> bike such as the fork and the spot in the back where the down tubes
> diverge.  Those aren't possible with blobs.

I wouldn't say that, bent tubes could be easily done with a lot of
spherical components.  Also several cylinders joining in one point are no
problem, but it would be quite difficult to do this with patches. 

Attached it the following:

blob
{
  threshold 0.5   
  cylinder { -z, z, 0.3, 1 }     
  cylinder { x*0.3, x, 0.3, 1 }
  sturm 
}

Using megapov's isosurface/isoblob object could be even more flexible, but
also more difficult to handle.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

Post a reply to this message

Attachments:
Download 'blobtest_01.jpg' (5 KB)

Preview of image 'blobtest_01.jpg'

Try looking at:

http://www.trekbikes.com/bikes/2001/road/5200_main.html

This is the bike that I am trying to make.  I personally find bezier patches to
be much more efficient and precise than blobs, and I also wanted to be able to
make non-elliptical tubes and use uv-mapping.  For these reasons, I personally
think that patches would make much more sense if there was a way around those
middle points.

 - Rico

Post a reply to this message

Reusser wrote:
> 
> Try looking at:
> 
> http://www.trekbikes.com/bikes/2001/road/5200_main.html
> 
> This is the bike that I am trying to make.  I personally find bezier patches to
> be much more efficient and precise than blobs, and I also wanted to be able to
> make non-elliptical tubes and use uv-mapping.  

more efficient - maybe
more precise - no way, bezier patches are internally converted to meshes
so they have a limited accuracy, while blobs are not (and most problems
with artefacts can be solved by adding 'sturm')

> For these reasons, I personally
> think that patches would make much more sense if there was a way around those
> middle points.

To do this you will have to describe the transit mathematically, probably
in form of a blob-like model - it would not look much different then in
the end.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

Post a reply to this message

On Mon, 25 Jun 2001 00:04:06 -0500, Reusser wrote:
>Here's the image illustrating my problem from povray.general.  In case
>you didn't see that one, I'm looking for a macro that eliminates the
>need to enter the red points manually in the bezier patch.  Thanks.

It looks like, for your application, you can just do simple addition.
If the corner is point "A" and the two adjacent edge points are "B" and
"C", then it would seem that the interior point adjacent to "B" and "C"
would be approximated by B+C-A.

-- 
plane{-z,-3normal{crackle scale.2#local a=5;#while(a)warp{repeat x flip x}rotate
z*60#local a=a-1;#end translate-9*x}pigment{rgb 1}}light_source{-9red 1rotate 60
*z}light_source{-9rgb y rotate-z*60}light_source{9-z*18rgb z}text{ttf"arial.ttf"
"RP".01,0translate-<.6,.4,.02>pigment{bozo}}light_source{-z*3rgb-.2}//Ron Parker

Post a reply to this message

Christoph Hormann wrote:

> more efficient - maybe
> more precise - no way, bezier patches are internally converted to meshes
> so they have a limited accuracy, while blobs are not (and most problems
> with artefacts can be solved by adding 'sturm')

By precise, I meant the control over the appearance, not necessarily the
mathematical precision.  Isn't there an accuracy setting anyway?  For me, the main
problem with blobs is that the transitions between the joints are too abrupt.  You
can see this in your example.  I was hoping to recreate the smooth, flowing look of
the frame.

 - Rico

Post a reply to this message

Ron Parker wrote:

> It looks like, for your application, you can just do simple addition.

Thanks!  I can't believe I didn't see that!  I was just thinking too hard, or not
hard enough.  :-)

 - Rico

Post a reply to this message

Reusser wrote:
> 
> By precise, I meant the control over the appearance, not necessarily the
> mathematical precision.  Isn't there an accuracy setting anyway?  For me, the main
> problem with blobs is that the transitions between the joints are too abrupt.  You
> can see this in your example.  I was hoping to recreate the smooth, flowing look of
> the frame.

Then maybe try an isosurface, like explained here (bottom of the page):

http://webpages.charter.net/omniverse/stb_iso/iso_tutorial3.html

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

Post a reply to this message