I just can't get this to work. Accuracy, method and max_gradient (over 2000)
have no effect at all. The artifact stays there.
  The right half of the front-side of the box is shadowed. It depends on
the location of the camera (eg. if the camera is moved a bit to the right, the
shadowed area moves as well).

  Another interesting effect happens when you uncomment the last light_source
in the example scene. Since it's inside the isosurface, it shouldn't illuminate
anything. However, it not only illuminates the isosurface itself but also
the floor.

  Any explanation / fix suggestion?

---------8<---------8<---------8<---------8<---------8<---------8<------
#version Unofficial MegaPov 0.6;

#declare ObjectFunc =
  function { pigment { boxed color_map { [0 rgb 1][0 rgb 0][1 rgb 0] } } }

isosurface
{ function { ObjectFunc(x,y,z) }
  contained_by { box { -1.01,1.01 } }
  max_gradient 2000
  threshold .5
  pigment { rgb x+y }
}

camera { location <0,5,-10>*.7 look_at 0 angle 35 }
light_source { <100,200,-150>, 1 }
plane { y,-1 pigment { checker rgb 1, rgb .5 } }
//light_source { 0, x }
---------8<---------8<---------8<---------8<---------8<---------8<------

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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Problably (once more) a precision problem.

try this:

function { pigment { boxed color_map { [0 rgb .51][0 rgb .49][1 rgb 0] }
} }

Bouf.

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Warp wrote in message <3a1e53fd@news.povray.org>...
> I just can't get this to work. Accuracy, method and max_gradient (over
2000)
> have no effect at all. The artifact stays there.

I have noticed the same problem.
first I prepare CSG than I declare function{pigment{object{...}}} to
describe interior of it
and then I clone this as isosurface. Isosurface has artifacts even with
accuracy 0.00005.
I have calculated value (with eval) of max_gradient as 200000 but this
not help. I read somewhere that pigments has smaller precision than
coordinates and pervaps this is cause.
I have also noticed that there is no hilights on iso-cloned object which
appear in original csg.
This means that normals are completely wrong.

ABX

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Warp wrote:
> 
>   I just can't get this to work. Accuracy, method and max_gradient (over 2000)
> have no effect at all. The artifact stays there.
> [...]
> #declare ObjectFunc =
>   function { pigment { boxed color_map { [0 rgb 1][0 rgb 0][1 rgb 0] } } }
> 

It's the old problem of abrupt changes (infinite gradient) in the
isosurface function.  In general the boxed pigment is well suited for
isosurface functions but with your color_map it has the same problem as
object pattern / crackle solid / ...

If you try 

function { pigment { boxed color_map { [0 rgb 1][k rgb 0][1 rgb 0] } } }

with 0.1 > k > 0.0 and check the max_gradient values (using eval), this
should become clear.

BTW, the max_gradient with k=0.0 purely depends on the accuracy.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
Homepage: http://www.schunter.etc.tu-bs.de/~chris/

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In article <3a1e6b2a@news.povray.org>, "Wlodzimierz ABX Skiba" 
<abx### [at] abxartpl> wrote:

> first I prepare CSG than I declare function{pigment{object{...}}} to 
> describe interior of it and then I clone this as isosurface. 
> Isosurface has artifacts even with accuracy 0.00005.
> I have calculated value (with eval) of max_gradient as 200000 but this
> not help.

The object pattern has two states: on and off. It doesn't have any 
"in-between" values. Patterns like this have an infinite gradient, and 
cause the isosurface algorithm problems. Other patterns that have this 
problem are checkers, hexagon, brick, and any pigment that has sharp 
lines. Warp is using the boxed pattern, which does vary smoothly, but 
his color_map is [0 rgb 1][0 rgb 0][1 rgb 0], which looks like a mistake 
to me...it is completely black, with no variation at all, basically a 
big, slow rendering 0. I think he wants [0 rgb 1][1 rgb 0] instead.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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In article <3a1e53fd@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

You declared your pigment as:
#declare ObjectFunc =
function {
    pigment {boxed
        color_map {[0 rgb 1][0 rgb 0][1 rgb 0]}
    }
}

What are you expecting this color_map to result in? It starts out as 
white, but goes to black in 0 distance and ends in black, basically a 
black pigment...isosurfaces require a smoothly varying function. My 
guess is you want either this:
color_map {[0 rgb 1][1 rgb 0]}
or something similar to this:
color_map {[0 rgb 1][0.5 rgb 0][1 rgb 0]}

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Chris Huff wrote in message ...
>In article <3a1e6b2a@news.povray.org>, "Wlodzimierz ABX Skiba"
><abx### [at] abxartpl> wrote:
>
> > first I prepare CSG than I declare function{pigment{object{...}}} to
> > describe interior of it and then I clone this as isosurface.
> > Isosurface has artifacts even with accuracy 0.00005.
> > I have calculated value (with eval) of max_gradient as 200000 but
this
> > not help.
>
> The object pattern has two states: on and off. It doesn't have any
> "in-between" values. Patterns like this have an infinite gradient, and
> cause the isosurface algorithm problems. Other patterns that have this
> problem are checkers, hexagon, brick, and any pigment that has sharp
> lines.

I know this but unfortunatly in current (unoficial) state of pov this is
only way to play with described week ago nonlinear transformations.
Everything is ok but normals.

hmmm

perhaps the problem can be resolved just like in smooth_triangle ?

in 2D description:

1. take point at equipotential surface
    P
2. take value at corners of cube around of it (size of cube depends of
accuracy)
   V1---V2
    |\ /|
    | P |
    |/ \|
   V3---V4
3. find points on edges where value is like in P
4. aproximate normal

ABX at babilon at org

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Wlodzimierz ABX Skiba wrote:
> 
> 
> I know this but unfortunatly in current (unoficial) state of pov this is
> only way to play with described week ago nonlinear transformations.
> Everything is ok but normals.
> 

I don't think so, AFAIK, every surface could somehow be approximated with
a smooth isosurface function, although it can be quite complicated and i
agree that it would be nice to use an object pattern for this purpose.

> perhaps the problem can be resolved just like in smooth_triangle ?
> 
> in 2D description:
> 
> 1. take point at equipotential surface
>     P
> 2. take value at corners of cube around of it (size of cube depends of
> accuracy)
>    V1---V2
>     |\ /|
>     | P |
>     |/ \|
>    V3---V4
> 3. find points on edges where value is like in P
> 4. aproximate normal

But there is no point in pigment { checker color rgb 0 color rgb 1 } where
the value is 0.5 so there is also no equipotential surface for this value.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
Homepage: http://www.schunter.etc.tu-bs.de/~chris/

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Christoph Hormann wrote in message
<3A1E8FCA.A806F53B@schunter.etc.tu-bs.de>...
> > I know this but unfortunatly in current (unoficial) state of pov
this is
> > only way to play with described week ago nonlinear transformations.
> > Everything is ok but normals.
>
> I don't think so, AFAIK, every surface could somehow be approximated
with
> a smooth isosurface function, although it can be quite complicated and
i
> agree that it would be nice to use an object pattern for this purpose.

I use this feature only to explore iso-functions possibilities of my
non-linear transformation. But if I want make usefull macro it should be
possible modify any object, not only described as functions. First one
is csg, second one is iso-non-linear-transformation, there is place for
third one but I'm working on it:
http://www.abx.art.pl/pov/nonlinear/twist.jpg

> But there is no point in pigment { checker color rgb 0 color rgb 1 }
where
> the value is 0.5 so there is also no equipotential surface for this
value.


hmmm

ABX at babilon at org

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Wlodzimierz ABX Skiba wrote:
> 
> I use this feature only to explore iso-functions possibilities of my
> non-linear transformation. But if I want make usefull macro it should be
> possible modify any object, not only described as functions. First one
> is csg, second one is iso-non-linear-transformation, there is place for
> third one but I'm working on it:
> http://www.abx.art.pl/pov/nonlinear/twist.jpg
> 

Every CSG made of cylinders, spheres, cones, boxes, torii should be quite
easy to convert to a smooth isosurface function, the more difficult things
are lathe, prism and meshes.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
Homepage: http://www.schunter.etc.tu-bs.de/~chris/

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