add tri_circumcircle

src/experimental/tri_circumcircle.scad

@@ -0,0 +1,18 @@
+function tri_circumcircle(points) =
+   let(
+      p0 = points[0],
+      p1 = points[1],
+      p2 = points[2],
+      v0 = p1 - p0,
+      d0 = (p1 + p0) / 2 * v0,
+      v1 = p2 - p1,
+      d1 = (p2 + p1) / 2 * v1,
+      det = -cross(v0 , v1)
+   )
+   det == 0? undef : 
+             let(
+                 x = (d1 * v0[1] - d0 * v1[1]) / det,
+                 y = (d0 * v1[0] - d1 * v0[0]) / det,
+                 r = norm(p0 - [x,y])
+             )
+             [[x,y], r];