When you get in close to an isosurface (at least one that's had an image map
/ picture impressed on it) you can see that it looks like a wireframe. Is
there a way to use POV-ray to write out that information as a mesh, or mesh
2?

You could then use POV-ray to do more complex wireframe/mesh modeling.

It would be a big help for those who want to animate isosurfaces.


normdoering

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normdoering <nor### [at] yahoocom> wrote:
> When you get in close to an isosurface (at least one that's had an image map
> / picture impressed on it) you can see that it looks like a wireframe.

  If it looks like a wireframe it doesn't mean it is a wireframe. It probably
means that your accuracy is too low.

-- 
#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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In article <web.3dc175b4282cec51d2ac4d730@news.povray.org>,
 "normdoering" <nor### [at] yahoocom> wrote:

> When you get in close to an isosurface (at least one that's had an image map
> / picture impressed on it) you can see that it looks like a wireframe. Is
> there a way to use POV-ray to write out that information as a mesh, or mesh
> 2?

You are mistaken. What you see are precision errors of the intersection 
solving algorithm, you probably just need to adjust your isosurface 
settings.
There is no wireframe information to write out. If there were, 
isosurfaces would be a lot faster.

-- 
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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You really can't put an isosurface to a wireframe.  You could create
approximations using an algorithm such as the marching cubes algorithm, but
it wouldn't be perfect.

I was once working on a macro that approximated an isosurface using a slight
variant of the marching cubes algorithm, but never quite finished it.
Parsing would take an extremely long time, especially if you wanted it to be
really accurate.  But the result would render very quickly compared to the
original isosurface.

-DJ

"normdoering" <nor### [at] yahoocom> wrote in message
news:web.3dc175b4282cec51d2ac4d730@news.povray.org...
>
> When you get in close to an isosurface (at least one that's had an image
map
> / picture impressed on it) you can see that it looks like a wireframe. Is
> there a way to use POV-ray to write out that information as a mesh, or
mesh
> 2?
>
> You could then use POV-ray to do more complex wireframe/mesh modeling.
>
> It would be a big help for those who want to animate isosurfaces.
>
>
> normdoering
>
>

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DJ Wiza wrote:
>You really can't put an isosurface to a wireframe.  You could create
>approximations using an algorithm such as the marching cubes algorithm, but
>it wouldn't be perfect.
>
>I was once working on a macro that approximated an isosurface using a slight
>variant of the marching cubes algorithm, but never quite finished it.
>Parsing would take an extremely long time, especially if you wanted it to be
>really accurate.  But the result would render very quickly compared to the
>original isosurface.
>
>-DJ

What are marching cubes?

I like modeling with isosurfaces, but less for the use of equations to make
shapes than for its height field like feature of being able to take an
image map, a picture I've drawn in Corel photopaint, or drawn with a pencil
and scanned. The problem with the height field is that it's always "flat."
Now, a height field looks like a wire frame too up close. Also, the basic
idea of using grey scale values as z values should be easy to implement.
What's needed is a way to bend, cut, join, and otherwise manipulate the
wire frames produced.

Drawing grey scale picture is a hell of a lot more efficient way of
generating a limited type of 3D data than trying to grab vertices with a
mouse and move them around in modelers like hamanapatch and what not.

Is there a way you could make height fields more flexible? Make it so you
can bend, wrap, join height field into a 3D object, like a head or skull?

Is what I'm asking clear?

Don't tell me a height field isn't a wireframe internally... It doesn't
matter, a grey scale picture should certainly easily become a wireframe.

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normdoering <nor### [at] yahoocom> wrote:
> Is there a way you could make height fields more flexible?

  Please see the section 7.13.1.1 of the POV-Ray 3.5 documentation.

> Don't tell me a height field isn't a wireframe internally...

  You talked about isosurfaces. Heightfields have nothing to do with that.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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> Is there a way you could make height fields more flexible? Make it so you
> can bend, wrap, join height field into a 3D object, like a head or skull?
>
> Is what I'm asking clear?
>
> Don't tell me a height field isn't a wireframe internally... It doesn't
> matter, a grey scale picture should certainly easily become a wireframe.


The code to render height fields is strongly based upon their rectangular
shape. The way it's coded, it's able to speed up the rendering a lot just by
making use of this fact. If you distort the height field's shape, you lose
this property and the height field will render at the same speed as a mesh.
Therefore, you might as well use a mesh. You should be able to write macros
that will take a function or pigment and create any shape mesh you want from
it in a height-field like fashion.

In fact, I believe there are macros for cylindrical and spherical height
fields in the standard include files somewhere.

 - Slime
[ http://www.slimeland.com/ ]

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Warp wrote:

> normdoering <nor### [at] yahoocom> wrote:
>> Is there a way you could make height fields more flexible?
> 
>   Please see the section 7.13.1.1 of the POV-Ray 3.5 documentation.
> 
>> Don't tell me a height field isn't a wireframe internally...
> 
>   You talked about isosurfaces. Heightfields have nothing to do with that.
> 

Well, height_fields indeed don't have anything to do with isosurfaces, but 
height fields in general do: a function of form y - my_height_func(x,0,z) 
produces one. And of course an isosurface height field is much more 
flexible than a traditional one.

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In article <web.3dca7ae6e6f4bb4af9811eb00@news.povray.org>,
 "normdoering" <nor### [at] yahoocom> wrote:

> What are marching cubes?

It's an algorithm for automatically creating a mesh from an arbitrary 
mathematically defined object. A patented method, actually...there are 
other similar non patented methods. The basic idea is to sample the idea 
on a 3D lattice to find connected points on its surface.


> Is there a way you could make height fields more flexible? Make it so you
> can bend, wrap, join height field into a 3D object, like a head or skull?

Doing so would lose the speed advantages of a height field, you might as 
well use a mesh. You could write macros to generate a mesh with all the 
distortions you want, look at the height field macros in shapes.inc for 
examples. Parsing will be slow, though.


> Don't tell me a height field isn't a wireframe internally... It doesn't
> matter, a grey scale picture should certainly easily become a wireframe.

It isn't, and it does matter. POV can't render wireframes, they are 
impossible to raytrace. Wireframe is a rendering method where lines 
(wires) are drawn to the image, not a kind of shape. Again, what you are 
seeing is simply a rendering error...in this case, one I've never seen.

-- 
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 wrote:

> Again, what you are seeing is simply a rendering error...
> in this case, one I've never seen.
>

He mentioned he's using image_map functions, so I think the "wireframe" 
effect is just pixelation...

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