andrew pressley elementary differential geometry
uad M = \mathbf{X}_{uv} \cdot \mathbf{N}, \quad N = \mathbf{X}_{vv} \cdot \mathbf{N} \] It measures the curvature of the surface at each point. Gaussian and Mean Curvature These curvatures are intrinsic and extrinsic measures of how a surface bends