I am having difficulty with the linear spline prism
with a conic sweep.  But before I issue a bug report,
I would appreciate it if someone could give this
test script a quick run to make sure I'm not doing
something stupid.....

This is supposed to be a closed truncated pyramid,
but instead I get an open truncated pyramid and a misplaced
face.  But please, check for yourself.

I am running 3.1r1 W95..... but I suspect this is a
core renderer problem (platform independent).

Dan

========================================

#declare V0 = <0, -3, 0>;
#declare V1 = V0 + <-5, 9, -8>;

camera {
  location V1
  look_at V0
}

light_source {
  V1
  color rgb 0.5
}
light_source {
  V1 * <-1, 1, 1>
  color rgb 0.5
}


prism {
  linear_spline
  conic_sweep
  -4, -2,
  4,
  <1, 1>, <-1, 1>, <-1, -1>, <1, -1>
  //open
  pigment { color rgb 1 } 
  finish { diffuse 0.5 ambient 0.5 }
}

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

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Dan Connelly wrote:

> I am having difficulty with the linear spline prism
> with a conic sweep.  But before I issue a bug report,
> I would appreciate it if someone could give this
> test script a quick run to make sure I'm not doing
> something stupid.....
>
> This is supposed to be a closed truncated pyramid,
> but instead I get an open truncated pyramid and a misplaced
> face.  But please, check for yourself.
>
> I am running 3.1r1 W95..... but I suspect this is a
> core renderer problem (platform independent).
>
> Dan
>
> ========================================
>
> #declare V0 = <0, -3, 0>;
> #declare V1 = V0 + <-5, 9, -8>;
>
> camera {  location V1  look_at V0}
>
> light_source {  V1  color rgb 0.5}
> light_source {  V1 * <-1, 1, 1>  color rgb 0.5}
>
> prism {  linear_spline  conic_sweep
>   -4, -2,  4,
>   <1, 1>, <-1, 1>, <-1, -1>, <1, -1>
>   //open
>   pigment { color rgb 1 }  finish { diffuse 0.5 ambient 0.5 }}
>
> ---
> http://www.flash.net/~djconnel/

  I can verify your problem but cannot explain it. If you change

prism {  linear_spline  conic_sweep
  -4, -2,  4,

to

prism {  linear_spline  conic_sweep
  -4, -1,  4,

it begins to appear as you want it to but the height
of the opening is higher and smaller  than you seem
to want.

The amount greater than -1 you use the more prevelent
the defect.

Ken Tyler

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Ken wrote:

>   I can verify your problem but cannot explain it. If you change
> 
> prism {  linear_spline  conic_sweep
>   -4, -2,  4,
> 
> to
> 
> prism {  linear_spline  conic_sweep
>   -4, -1,  4,
> 
> it begins to appear as you want it to but the height
> of the opening is higher and smaller  than you seem
> to want.
> 
> The amount greater than -1 you use the more prevelent
> the defect.

Ken :

Thanks for the quick help!!!  Yes -- it appears
there is in fact a bug.

I checked it so far on 3.1, 3.1 SuperPatch, and 3.02 TMPOV,
all of which yield identical results....

I will thus report it to bugreports, and use polygons instead
to achieve the shape I want.

Dan




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

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Dan Connelly wrote:
> 

> 
> This is supposed to be a closed truncated pyramid,
> but instead I get an open truncated pyramid and a misplaced
> face.  But please, check for yourself.
> 
> [some code].......

bug or feature?, that is here the question (freely by W. Shakespeare)

fact is, that in case of conic_sweep, you have by no way the freedom in
definition of the corner points of your prism, the docs want to make
believe you.
This all has to be done in a way, that at y = 1 your corner points ought
to have uv coordinates in a range between <-0.5, 0.5> and <0.5, 0.5>,
otherwise the inside of your prism apparently will be turned out and you
will get the open truncated pyramide and the misplaced face, you have
observed.
You should scale your prism afterwards.

Try out this, it works:

//pov code:

prism {linear_spline conic_sweep 1, 0.7, 5
       <-0.5, -0.5>, <0.5, -0.5>, <0.5, 0.5>, <-0.5, 0.5>, <-0.5, -0.5>
       pigment {Blue}
       translate <0, -0.85, 0>
       scale <5, 2, 3>
       rotate <0, 0, 180>
       }

//end of pov code


ReVerSi

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Thanks for the help!! There also seems to be a problem with the
negative axis positions..... but at least it is clear
with some algebraic manipulation I will be able to construct
the shape I want.

Dan

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

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