====== Rototraslazione sistema riferimento ======

$$x' = \cos \theta \, x + \sin \theta \, y + \left( - x_G \, \cos \theta - y_G \, \sin \theta  \right) \\
y' = - \sin \theta \, x + \cos \theta \, y + \left( x_G \, \sin \theta - y_G \, \cos \theta  \right) $$