public Point translate(Point delta) {
Point p = toUnit(delta.unit);
p.x += delta.x;
p.y += delta.y;
p.z += delta.z;
return p;
}
public Point diff(Point p) {
p = p.toUnit(unit);
p.x -= x;
p.y -= y;
p.z -= z;
return p;
}
