2 questions.

1) Anyone know of a web tutorial or information on modelling celestial
bodies? (moons, planets, etc.) and how to achieve a realistic eclipsed
effect?

2) How do I model say a spiral of beads or something?  I guess I would need
to use a polar equation with spheres spaced along the motion path of said
3-d polar equation?



Mike Metheny
lon### [at] vtedu
http://loneshepherd.ml.org/

"When one's words are no better than silence, one should keep silent."

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Mike Metheny wrote:
> 
> 2 questions.
> 
> 1) Anyone know of a web tutorial or information on modelling celestial
> bodies? (moons, planets, etc.) and how to achieve a realistic eclipsed
> effect?

Someone around here has a physicaly correct motions for planets
include file. I seem to recall that it was posted in one of the
scene files or utilities groups but may be wrong about that.

 
> 2) How do I model say a spiral of beads or something?  I guess I would need
> to use a polar equation with spheres spaced along the motion path of said
> 3-d polar equation?
> 
> Mike Metheny
> lon### [at] vtedu
> http://loneshepherd.ml.org/
> 
> "When one's words are no better than silence, one should keep silent."

For spiraling beeds you can set that up fairly easily with a loop.
Try changing values for #while and values for translate and rotate
to see the effects they have.

camera{location<0,0,-25>look_at 0}
light_source{<0,0,-400>,1}

// start loop at zero
#declare aa=0; 

// set counter amount
 #while  (aa<36) 


   // a union of objects to twist. As they are not as origin they
   // will orbit as they are rotated
   union{  
    sphere{<-.5,0, .5>,0.5}
    sphere{< .5,0, .5>,0.5}
    sphere{<-.5,0,-.5>,0.5}
     pigment{rgb 1}
      finish{specular .5}

    //sets the rotation amount: count 36 x 10 = 360 or 1 full twyst
     rotate y*10*aa 

// to center object on screen
    translate y*-10  

// translate in the +y direction as object is rotating
  translate<0,.5*aa,0>

 //end union
}

//  adds + 1 for each tick of the while counter so it will
//  not loop endlessly - ie stops when count reaches 36
#declare aa=aa+1; 

// end of loop
#end

After you play with this for a while throw it away and go see the
tutorials at spake.org. There is a set of six tutorials that cover
#unions, #while, #if, #next, #case, etc. They are written to be
understood for the most part by beginners but it takes a while to
get past the sheer volume they throw at you all at once. I sent the
pages to my email and studied them of line with pov open :)

http://www.spake.org/rtimes/


Hope this helps.


-- 
Ken Tyler

tyl### [at] pacbellnet

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Ken <tyl### [at] pacbellnet> wrote:
:> 2) How do I model say a spiral of beads or something?

: For spiraling beeds you can set that up fairly easily with a loop.

  If you just want a spiral galaxy you may also use just the spiral
pigment type (as used in Colefax's galaxy include file).

-- 
main(i){char*_="BdsyFBThhHFBThhHFRz]NFTITQF|DJIFHQhhF";while(i=
*_++)for(;i>1;printf("%s",i-70?i&1?"[]":" ":(i=0,"\n")),i/=2);} /*- Warp. -*/

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