18
Jul
05

### Kleinian Double Spiral

This is a stereographic projection of a Riemann sphere. This can be accomplished by applying a special homography to a single spiral. Click here to see a slightly different animation. Click here to download a Mathematica notebook for this image. See also my Double Cusp Group.
```(* runtime: 23 seconds *) Show[Graphics[RasterArray[Table[r1 = (x - 1)^2 + y^2; r2 = (x + 1)^2 + y^2; Hue[(Sign[y]ArcCos[(x^2 + y^2 - 1)/Sqrt[r1 r2]] -Log[r1/r2])/(2Pi)], {x, -2, 2, 4/274}, {y, -2, 2, 4/274}]], AspectRatio -> 1]]```

This is how you can make this in POV-Ray:
```// runtime: 2 seconds camera{orthographic location <0,0,-2> look_at 0 angle 90} #declare r1=function(x,y) {(x-1)*(x-1)+y*y}; #declare r2=function(x,y) {(x+1)*(x+1)+y*y}; #declare f=function{(y/abs(y)*acos((x*x+y*y-1)/sqrt(r1(x,y)*r2(x,y)))-ln(r1(x,y)/r2(x,y)))/(2*pi)}; plane{z,0 pigment{function{f(x,y,0)}} finish{ambient 1}}```

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