b = 500;
h = 500;
s =  2.0; // s>1 (nach aussen), s<1 (nach innen)
R =   30;
$ = '<svg width="550" height="550" viewBox="0 0 550 550" xmlns="http://www.w3.org/2000/svg"         \n';
$ = '     xmlns:xlink="http://www.w3.org/1999/xlink"> \n';

$ = '<path d="m ',b/2.,' ',h/2.-R,'\n';

w  = 90/360*2*PI; //  Winkel
xa = 0;
ya = R;
r  = R;

for (i=-1;i<=40;++i)
{
  r = r * 12 wurzel s;
  w = w-30./360*2*PI  ;
  x = cos w * r    ;
  y = sin w * r    ;
  $ = 'a ',r,' ',r,' 0 0 1 ',x-xa,' ',-y+ya,'\n';
  xa = x;
  ya = y;
}

$ = '" style="fill:white;stroke:red;stroke-width:1"/>\n';
$ = '</svg>\n';