A two dimensional surface that extends infinitely in 3d space, represented in [link:http://mathworld.wolfram.com/HessianNormalForm.html Hessian normal form]
by a unit length normal vector and a constant.
在三维空间中无限延伸的二维平面,平面方程用单位长度的法向量和常数表示为海塞法向量[link:http://mathworld.wolfram.com/HessianNormalForm.html Hessian normal form]形式。