Hesse normal form


The Hesse normal form named after Otto Hesse, is an equation used in analytic geometry, and describes a line in or a plane in Euclidean space or a hyperplane in higher dimensions. It is primarily used for calculating distances.
It is written in vector notation as
The dot indicates the scalar product or dot product.
The vector represents the unit normal vector of E or g, that points from the origin of the coordinate system to the plane. The distance is the distance from the origin to the plane.
This equation is satisfied by all points P, lying precisely in the plane E, described by the location vector that points from the origin of the coordinate system to P.

Derivation/Calculation from the normal form

Note: For simplicity, the following derivation discusses the 3D case. However, it is also applicable in 2D.
In the normal form,
a plane is given by a normal vector as well as an arbitrary position vector of a point. The direction of is chosen to satisfy the following inequality
By dividing the normal vector by its magnitude, we obtain the unit normal vector
and the above equation can be rewritten as
Substituting
we obtain the Hesse normal form

In this diagram, d is the distance from the origin. Because holds for every point in the plane, it is also true at point Q, with, per the definition of the Scalar product
The magnitude of is the shortest distance from the origin to the plane.