I faintly remember that someone had problems with trace() and isosurfaces.
I paid no much attention to that thread, but now I have the same problem.

  I have made the case as simple as possible. It seems that trace() doesn't
work with isosurfaces which use method 2.
  In the following code the trace() with the real torus returns <-2,1,0>
while the trace() with an equivalent isosurface returns <0,0,0>. If you
change the method to 1, it will return (approximately) the same:

#version Unofficial MegaPov 0.5;

$R1=2;
$R2=1;

$Torus1 = torus { R1, R2 }

$Torus2 =
  isosurface
  { function
    { sqrt(sqr(sqrt(sqr(x)+sqr(z))-R1)+sqr(y))-R2
    }
    method 2
    contained_by { sphere { 0,R1+R2 } }
  }

$P1 = trace(Torus1, <-R1,R2*2,0>, -y);
$P2 = trace(Torus2, <-R1,R2*2,0>, -y);

#debug concat("<",str(P1.x,0,-1),",",str(P1.y,0,-1),",",str(P1.z,0,-1),">\n")
#debug concat("<",str(P2.x,0,-1),",",str(P2.y,0,-1),",",str(P2.z,0,-1),">\n")


  In my scene the isosurface is more complex and seems to work well only
with method 2 (method 1 causes holes in the surface).

-- 
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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On 25 Jul 2000 11:09:14 -0400, Warp wrote:
>  I faintly remember that someone had problems with trace() and isosurfaces.
>I paid no much attention to that thread, but now I have the same problem.

I can duplicate this, but it doesn't make sense yet.

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
My opinions.  Mine.  Not anyone else's.

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Warp wrote:
> 
>   I faintly remember that someone had problems with trace() and isosurfaces.
> I paid no much attention to that thread, but now I have the same problem.

It may not be of much help, but which OS are you using ?  The person
who had the problem was using some Ux flavour.

Using the W95 version, I managed to successfully use trace() on a
ridged multifractal, method 2.  (and I also had success with the
code that person provided).

Might be a version-specific problem...

Fabien.

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On Tue, 25 Jul 2000 21:48:39 +0200, Fabien Mosen wrote:
>Warp wrote:
>> 
>>   I faintly remember that someone had problems with trace() and isosurfaces.
>> I paid no much attention to that thread, but now I have the same problem.
>
>It may not be of much help, but which OS are you using ?  The person
>who had the problem was using some Ux flavour.
>
>Using the W95 version, I managed to successfully use trace() on a
>ridged multifractal, method 2.  (and I also had success with the
>code that person provided).
>
>Might be a version-specific problem...

I duplicated it on Win MegaPOV 0.3.

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
My opinions.  Mine.  Not anyone else's.

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Appending the following code to the code you provided, it works
perfectly well in my MegaPOV 0.5A, Win95.  Hope this could help in
debugging purposes.

#include "colors.inc"

camera {location <10,10,10> direction z*1 look_at <0,0,0>}

object {Torus2 pigment {White}}

#declare MinX=-5;
#declare MinZ=-5;
#declare MaxX=5;
#declare MaxZ=5;
#declare ScanStep=.5;
#declare ScanHeight=5;
#declare StockNormal=<0,0,0>;

#declare I=MinX;
#while (I < MaxX)
 #declare J=MinZ;
 #while (J < MaxZ)
   #declare FoundPoint = 
    trace (Torus2,<I,ScanHeight,J>,-y,StockNormal);  
 
    disc {FoundPoint,StockNormal,.15 pigment {Red}}
 
 #declare J=J+ScanStep;
 #end
#declare I=I+ScanStep;
#end

light_source {<400,500,300> White*2}

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No, it doesn't seem to work (at least not here). All the discs are put
at <0,0,0>.

-- 
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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