Hi,

I was working on creating a scene for POV-Comp using POV-Ray
3.6.1.icl8.win32 and came across this interesting behavior.

I am trying to declare an object that is rotated at some random angle around
an axis.  I need to create many of them so I declared a single instance
first then used a #while loop to create all of them.

I've found that if I include my rotate in the declaration, it doesn't make
it to the final object for some reason, but if I include it in the while
object declaration, it does.  Is this what's supposed to happen?

Sample code:

#declare R1=seed(0);

camera{
 location <0,00,-3>
 look_at <0,0,0>
}

#declare pole=
 cylinder{
  <0,0,0>,<0,1,0>,.01
  rotate <0,0,rand(R1)*360>
  pigment{
   rgb 1
  }
  finish{
   ambient 1
  }
 }
;

#declare c=100;
#while (c>0)
 object{
  pole
  translate <-1,0,0>
 }
 #declare c=c-1;
#end

#declare c=100;
#while (c>0)
 object{pole
  rotate <0,0,rand(R1)*360>
  translate <1,0,0>
 }
 #declare c=c-1;
#end

Post a reply to this message

hi,

The problem is as follows:

in the 1st version, where you declare the object first and rotate "within"
the declare statement, it DOES rotate. But what you really want, is to have
it rotate randomly (?). This, it doesn't. It rotates around a fixed angle
defined by the first (and only) time you use Rrand().

in the 2nd version the angle is calculated EACH time the while loop reaches
Rrand(), and therefore the objects rotate around different angles.

So, yes, what you see is perfectly correct :-).

Hoping to be of help,

JWV


"N Shomber" <nsh### [at] hotmailcom> wrote in message
news:41225b60$1@news.povray.org...
> Hi,
>
> I was working on creating a scene for POV-Comp using POV-Ray
> 3.6.1.icl8.win32 and came across this interesting behavior.
>
> I am trying to declare an object that is rotated at some random angle
around
> an axis.  I need to create many of them so I declared a single instance
> first then used a #while loop to create all of them.
>
> I've found that if I include my rotate in the declaration, it doesn't make
> it to the final object for some reason, but if I include it in the while
> object declaration, it does.  Is this what's supposed to happen?
>
> Sample code:
>
> #declare R1=seed(0);
>
> camera{
>  location <0,00,-3>
>  look_at <0,0,0>
> }
>
> #declare pole=
>  cylinder{
>   <0,0,0>,<0,1,0>,.01
>   rotate <0,0,rand(R1)*360>
>   pigment{
>    rgb 1
>   }
>   finish{
>    ambient 1
>   }
>  }
> ;
>
> #declare c=100;
> #while (c>0)
>  object{
>   pole
>   translate <-1,0,0>
>  }
>  #declare c=c-1;
> #end
>
> #declare c=100;
> #while (c>0)
>  object{pole
>   rotate <0,0,rand(R1)*360>
>   translate <1,0,0>
>  }
>  #declare c=c-1;
> #end
>
>

Post a reply to this message

JWV is right. You'll have the same problem if you use some random noise in a
isosurface or a texture. I usually change #declare by #macro that are
processed at render time and not at parse time. Try this:

#macro pole()
 cylinder{
  <0,0,0>,<0,1,0>,.01
  rotate <0,0,rand(R1)*360>
  pigment{
   rgb 1
  }
  finish{
   ambient 1
  }
 }
#end

#declare c=100;
#while (c>0)
 object{
  pole()
  translate <-1,0,0>
 }
 #declare c=c-1;
#end

.Groucho.

"JWV" <jwv|at|planet.nl> wrote in message news:41225d79@news.povray.org...
> hi,
>
> The problem is as follows:
>
> in the 1st version, where you declare the object first and rotate "within"
> the declare statement, it DOES rotate. But what you really want, is to
have
> it rotate randomly (?). This, it doesn't. It rotates around a fixed angle
> defined by the first (and only) time you use Rrand().
>
> in the 2nd version the angle is calculated EACH time the while loop
reaches
> Rrand(), and therefore the objects rotate around different angles.
>
> So, yes, what you see is perfectly correct :-).
>
> Hoping to be of help,
>
> JWV
>
>
> "N Shomber" <nsh### [at] hotmailcom> wrote in message
> news:41225b60$1@news.povray.org...
> > Hi,
> >
> > I was working on creating a scene for POV-Comp using POV-Ray
> > 3.6.1.icl8.win32 and came across this interesting behavior.
> >
> > I am trying to declare an object that is rotated at some random angle
> around
> > an axis.  I need to create many of them so I declared a single instance
> > first then used a #while loop to create all of them.
> >
> > I've found that if I include my rotate in the declaration, it doesn't
make
> > it to the final object for some reason, but if I include it in the while
> > object declaration, it does.  Is this what's supposed to happen?
> >
> > Sample code:
> >
> > #declare R1=seed(0);
> >
> > camera{
> >  location <0,00,-3>
> >  look_at <0,0,0>
> > }
> >
> > #declare pole=
> >  cylinder{
> >   <0,0,0>,<0,1,0>,.01
> >   rotate <0,0,rand(R1)*360>
> >   pigment{
> >    rgb 1
> >   }
> >   finish{
> >    ambient 1
> >   }
> >  }
> > ;
> >
> > #declare c=100;
> > #while (c>0)
> >  object{
> >   pole
> >   translate <-1,0,0>
> >  }
> >  #declare c=c-1;
> > #end
> >
> > #declare c=100;
> > #while (c>0)
> >  object{pole
> >   rotate <0,0,rand(R1)*360>
> >   translate <1,0,0>
> >  }
> >  #declare c=c-1;
> > #end
> >
> >
>
>

Post a reply to this message

Thanks

-Nathan

"Groucho" <jca### [at] terraes> wrote in message
news:4122614e$1@news.povray.org...
> JWV is right. You'll have the same problem if you use some random noise in
a
> isosurface or a texture. I usually change #declare by #macro that are
> processed at render time and not at parse time. Try this:
>
> #macro pole()
>  cylinder{
>   <0,0,0>,<0,1,0>,.01
>   rotate <0,0,rand(R1)*360>
>   pigment{
>    rgb 1
>   }
>   finish{
>    ambient 1
>   }
>  }
> #end
>
> #declare c=100;
> #while (c>0)
>  object{
>   pole()
>   translate <-1,0,0>
>  }
>  #declare c=c-1;
> #end
>
> .Groucho.
>
> "JWV" <jwv|at|planet.nl> wrote in message news:41225d79@news.povray.org...
> > hi,
> >
> > The problem is as follows:
> >
> > in the 1st version, where you declare the object first and rotate
"within"
> > the declare statement, it DOES rotate. But what you really want, is to
> have
> > it rotate randomly (?). This, it doesn't. It rotates around a fixed
angle
> > defined by the first (and only) time you use Rrand().
> >
> > in the 2nd version the angle is calculated EACH time the while loop
> reaches
> > Rrand(), and therefore the objects rotate around different angles.
> >
> > So, yes, what you see is perfectly correct :-).
> >
> > Hoping to be of help,
> >
> > JWV
> >
> >
> > "N Shomber" <nsh### [at] hotmailcom> wrote in message
> > news:41225b60$1@news.povray.org...
> > > Hi,
> > >
> > > I was working on creating a scene for POV-Comp using POV-Ray
> > > 3.6.1.icl8.win32 and came across this interesting behavior.
> > >
> > > I am trying to declare an object that is rotated at some random angle
> > around
> > > an axis.  I need to create many of them so I declared a single
instance
> > > first then used a #while loop to create all of them.
> > >
> > > I've found that if I include my rotate in the declaration, it doesn't
> make
> > > it to the final object for some reason, but if I include it in the
while
> > > object declaration, it does.  Is this what's supposed to happen?
> > >
> > > Sample code:
> > >
> > > #declare R1=seed(0);
> > >
> > > camera{
> > >  location <0,00,-3>
> > >  look_at <0,0,0>
> > > }
> > >
> > > #declare pole=
> > >  cylinder{
> > >   <0,0,0>,<0,1,0>,.01
> > >   rotate <0,0,rand(R1)*360>
> > >   pigment{
> > >    rgb 1
> > >   }
> > >   finish{
> > >    ambient 1
> > >   }
> > >  }
> > > ;
> > >
> > > #declare c=100;
> > > #while (c>0)
> > >  object{
> > >   pole
> > >   translate <-1,0,0>
> > >  }
> > >  #declare c=c-1;
> > > #end
> > >
> > > #declare c=100;
> > > #while (c>0)
> > >  object{pole
> > >   rotate <0,0,rand(R1)*360>
> > >   translate <1,0,0>
> > >  }
> > >  #declare c=c-1;
> > > #end
> > >
> > >
> >
> >
>
>

Post a reply to this message