public BiFace(Point3D p0, Point3D p1) {
this.p0 = p0;
this.p1 = p1;
double x = p1.x() - p0.x();
double y = p1.y() - p0.y();
n = new Vector3D(y, -x, 0);
n = n.mult(1 / n.norm2());
}
public double getArea() {
Vector3D a = new Vector3D(p0, p1);
return a.norm2();
}