/**
* computes the angle difference between a and b as viewed from center
*
* @param center
* @param a
* @param b
* @return angle
*/
public static double computeObservedAngle(Point2D center, Point2D a, Point2D b) {
Point2D da = Geometry.diff(a, center);
Point2D db = Geometry.diff(b, center);
double angle = Math.abs(Geometry.computeAngle(da) - Geometry.computeAngle(db));
if (angle > Math.PI) angle = 2 * Math.PI - angle;
double det = da.getX() * db.getY() - da.getY() * db.getX();
if (det >= 0) return angle;
else return -angle;
}
/**
* computes the angle difference between a and b as viewed from center
*
* @param center
* @param a
* @param b
* @return angle
*/
public static double basicComputeAngle(Point2D center, Point2D a, Point2D b) {
Point2D da = Geometry.diff(a, center);
Point2D db = Geometry.diff(b, center);
return Geometry.moduloTwoPI(Geometry.computeAngle(db) - Geometry.computeAngle(da));
}