Star

The construction of a simple star shape.
Example for the using of the "intersection" and/or "difference".
Objects:   "box", "sphere".
Methods: "#declare", "union{...}", "intersection", "difference".
Click here for an example!

The construction step by step:

We start with a "box". To get a clearly defined length of the rays we scale the box by the square root of 2. (Then the diagonals of it's surfaces have a length of 2 units!)

  box { <-1,-1,-1>,< 1,1,1>
        scale <1,1,1>*sqrt(2)
      }

We rotate the box around the z axis by 45 degrees.

  box { <-1,-1,-1>,< 1,1,1>
        scale <1,1,1>*sqrt(2)
        rotate<0,0,45>
      }

Then the box is scaled in y direction and after this it is turned around the x axis by 45 degrees. We use the declare statement to make this shape now to a new object called "Ray_Profile".

  #declare Ray_Profile =
   box { <-1,-1,-1>,< 1,1,1>
        scale <1,1,1>*sqrt(2)
        rotate<0,0,45>
        scale <1,0.36,1>
        rotate<45,0,0>
      }

The new object is now mirrored at the xy plane in z direction by "scale<1,1,-1>". Then we make an intersection of the original shape and it's mirror image..

 intersection{
   object{ Ray_Profile }
   object{ Ray_Profile scale<1,1,-1>}
   }

To be able to make also stars with an odd number of rays we need to subtract ( = intersection with the inverse shape) a box to get rid of the left part of our ray shape. This shape now we declare as a new object called "'Ray"..

#declare Ray =
 intersection{
   object{ Ray_Profile }
   object{ Ray_Profile scale<1,1,-1>}
   box{<-2,-1,-1>,<0,1,1> inverse}
   }

The rays of a star were arranged finally by a while loop rotating them around the y axis. For the right image the rays were made more slender by applying " scale<1,0,5,0.5> ".
The resulting star shape has a radius of 2 units.

union{
 #local Nr = 0;     // start
 #local EndNr = 5;  // end
 #while (Nr < EndNr)
 object{Ray rotate<0,Nr*360/EndNr,0>}
 #local Nr = Nr + 1;// next Nr
 #end // ------------- end of loop
rotate<0,0,0>
translate<0,0,0>
} // end of union

Scene file for POV-Ray:
"star0.txt" or "star0.pov"