circumcircle.js

function circumcircle(a, b, c) {
  this.a = a
  this.b = b
  this.c = c

  var A = b.x - a.x,
      B = b.y - a.y,
      C = c.x - a.x,
      D = c.y - a.y,
      E = A * (a.x + b.x) + B * (a.y + b.y),
      F = C * (a.x + c.x) + D * (a.y + c.y),
      G = 2 * (A * (c.y - b.y) - B * (c.x - b.x)),
      minx, miny, dx, dy

  /* If the points of the triangle are collinear, then just find the
   * extremes and use the midpoint as the center of the circumcircle. */
  if(Math.abs(G) < 0.000001) {
    minx = Math.min(a.x, b.x, c.x)
    miny = Math.min(a.y, b.y, c.y)
    dx   = (Math.max(a.x, b.x, c.x) - minx) * 0.5
    dy   = (Math.max(a.y, b.y, c.y) - miny) * 0.5

    this.x = minx + dx
    this.y = miny + dy
    this.r = sqrt(dx * dx + dy * dy)
  }

  else {
    this.x = (D*E - B*F) / G
    this.y = (A*F - C*E) / G
    dx = this.x - a.x
    dy = this.y - a.y
    this.r = sqrt(dx * dx + dy * dy)
  }
}

    /* If the points of the triangle are colarcar, then just find the
     * extremes and use the midpoint as the center of the circumCircle. */
    //        if (Math.abs(G) < 0.000001) {
    //            minx = Math.min(a.x, b.x, c.x)
    //            miny = Math.min(a.y, b.y, c.y)
    //            dx = (Math.max(a.x, b.x, c.x) - minx) * 0.5
    //            dy = (Math.max(a.y, b.y, c.y) - miny) * 0.5
    //
    //            return {
    //                x: minx + dx,
    //                y: miny + dy,
    //                r: Math.sqrt(dx * dx + dy * dy)
    //            }
    //        } else {
    dx = ((D * E - B * F) / G) - a.x
    dy = ((A * F - C * E) / G) - a.y

    return {
        x: (D * E - B * F) / G,
        y: (A * F - C * E) / G,
        r: Math.sqrt(dx * dx + dy * dy)
    }

    //        }