This .NET class wraps the AcGePlanarEnt ObjectARX class. 

The class PlanarEnt is an abstract base class for all planar surfaces. Any planar surface S is parameterized the following way: parameter point with coordinates u,v maps to the modeling space point S(u,v) by the formula. 

S(u,v) = originOfPlanarEntity + u * uAxis + v * vAxis

Vectors uAxis, vAxis are not assumed to be either normalized or perpendicular, but they must be non-collinear. Parameterization of the planar entity is invariant under affine transformations; that is, if planar surface S2 is the result of affine transformation of a planar surface S1, then point S1(u,v) is mapped to the point S2(u,v) by the same affine transformation. 

There is an orthonormal coordinate system in the plane of any planar surface associated with it in the following way: 

• origin is originOfPlanarEntity
• axis1 is uAxis.normal()
• axis2 is uAxis.crossProduct(vAxis).normal()

This coordinate system is called the canonical coordinate system of the planar entity.

Autodesk.AutoCAD.Geometry.Entity3d
    Autodesk.AutoCAD.Geometry.Surface
        Autodesk.AutoCAD.Geometry.PlanarEntity
            Autodesk.AutoCAD.Geometry.BoundedPlane
            Autodesk.AutoCAD.Geometry.Plane

Public abstract Class PlanarEntity
Inherits Surface

public abstract class PlanarEntity : Surface;