@property
    @_memo
    def face_areas(self):
        """Area of each face.
        """
        # Compute normal vector (length is face area)
        nnfnorms = np.cross(self.ppts[:,1] - self.ppts[:,0], 
                            self.ppts[:,2] - self.ppts[:,0])
        # Compute vector length
        return np.sqrt((nnfnorms**2).sum(-1)) / 2
dataset/ETHPy150Open gallantlab/pycortex/cortex/polyutils.py/Surface.face_areas/original