/** returns the factor index for the statistics array */
 public static int getFactorIndex(Wave wave, Point2D.Double target) {
   double offsetAngle = (absoluteBearing(wave.getOrigin(), target) - wave.getAngle());
   double factor =
       Utils.normalRelativeAngle(offsetAngle)
           / maxEscapeAngle(wave.getVelocity())
           * wave.getDirection();
   return computeBin(factor);
 }