I was trying to figure out how to warp a cylinder into a sphere sweep
helix, but it didn't work.  It squished the thing for some reason.  My
thought was to turn the x dimension of the cylinder into the radius, and
the y dimension into the angle, but everything needs to be done
backwards.  I was trying to use a rectangular to polar conversion
formula, because of things needing to be backwards.  

I would appreciate it if someone could tell how to do it right.  I would
also like to know how to do the same thing using parametic surfaces, and
what it was that I was doing wrong.  

I think this is the code I was using.  

#include "colors.inc"
#include "finish.inc"
light_source {<3,4,-5>*100 rgb 2}
camera {location <12,0,-14> look_at 0 }

#version unofficial MegaPov 0.7;

#declare Cyl= function{((x-3)^2+y^2)^.5 -1}
//plane{y,-2 pigment{White}}
#declare Cyl2 =  function {Cyl(x,z*cos(pi/3) - y*sin(pi/3),
  y*cos(pi/3) + z*sin(pi/3))}
#declare Cir = function{(x*cos(y)+x*sin(y))}
#declare Cir2 = function{Cyl2(sqr(x^2+y^2),atan2(x,y),z)}

isosurface{
   function {Cir2(x,y,z)}
    contained_by{box{-2*pi,2*pi}}
    method 2
    eval
    pigment{Green}
    finish{Shiny}
   }

-- 
Dan Johnson 

http://www.geocities.com/zapob

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Dan Johnson wrote:
> 
> I was trying to figure out how to warp a cylinder into a sphere sweep
> helix, but it didn't work.  It squished the thing for some reason.  My
> thought was to turn the x dimension of the cylinder into the radius, and
> the y dimension into the angle, but everything needs to be done
> backwards.  I was trying to use a rectangular to polar conversion
> formula, because of things needing to be backwards.
> 
> I would appreciate it if someone could tell how to do it right.  I would
> also like to know how to do the same thing using parametic surfaces, and
> what it was that I was doing wrong.
> 

Why don't you use a built in helix function:

http://users.skynet.be/smellenbergh/buildin.html#Helix1

You can of course do it by hand, but this is a bit complicated, have a
look at the megapov source if you want to know.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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> 
> Why don't you use a built in helix function:

Can I blob together the built in function?  I did know there is a built
in function, but that takes the understanding out of it.  
> 
> http://users.skynet.be/smellenbergh/buildin.html#Helix1
> 
> You can of course do it by hand, but this is a bit complicated, have a
> look at the megapov source if you want to know.

Do you mean the C source code, or scene description language?
> 
> Christoph
> 
> --
> Christoph Hormann <chr### [at] gmxde>
> IsoWood include, radiosity tutorial, TransSkin and other
> things on: http://www.schunter.etc.tu-bs.de/~chris/


-- 
Dan Johnson 

http://www.geocities.com/zapob

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Dan Johnson wrote:
> 
> >
> > Why don't you use a built in helix function:
> 
> Can I blob together the built in function?  
> 

Why not?

> > You can of course do it by hand, but this is a bit complicated, have a
> > look at the megapov source if you want to know.
> 
> Do you mean the C source code, or scene description language?

The C source (it's the file 'isofunc.c' in megapov)

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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Dan Johnson wrote:
> 
> I was trying to figure out how to warp a cylinder into a sphere sweep
> helix, but it didn't work.  It squished the thing for some reason.  My
> thought was to turn the x dimension of the cylinder into the radius, and
> the y dimension into the angle, but everything needs to be done
> backwards.  I was trying to use a rectangular to polar conversion
> formula, because of things needing to be backwards.
> 
> I would appreciate it if someone could tell how to do it right.  I would
> also like to know how to do the same thing using parametic surfaces, and
> what it was that I was doing wrong.
> 
> I think this is the code I was using.
> 
> #include "colors.inc"
> #include "finish.inc"
> light_source {<3,4,-5>*100 rgb 2}
> camera {location <12,0,-14> look_at 0 }
> 
> #version unofficial MegaPov 0.7;
> 
> #declare Cyl= function{((x-3)^2+y^2)^.5 -1}
> //plane{y,-2 pigment{White}}
> #declare Cyl2 =  function {Cyl(x,z*cos(pi/3) - y*sin(pi/3),
>   y*cos(pi/3) + z*sin(pi/3))}
> #declare Cir = function{(x*cos(y)+x*sin(y))}
> #declare Cir2 = function{Cyl2(sqr(x^2+y^2),atan2(x,y),z)}

I just had a very brief look at your code,
and right now I don't know if what you are
doing here are the right way to go.
(I'm not even sure if I understand what
shape you are trying make. Maybe I can
look at it tomorrow.)

BUT if you are doing conversion from
rectangular to polar coordinates, then
this expression looks suspicious:

> #declare Cir2 = function{Cyl2(sqr(x^2+y^2),atan2(x,y),z)}

Shouldn't sqr(x^2+y^2) be sqrt(x^2 + y^2) ?


And this function:

> #declare Cir = function{(x*cos(y)+x*sin(y))}

is equivalent to this function:

#declare Cir = function { x*(cos(y) + sin(y)) }

Was that your intention ?


Tor Olav

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