Project a 3d vector onto a plane, convert 3D to 2D vector, useful for rendering a 2D indicator over 3D element or get direction of 3D element if out of frame

Project3dVectorOnToPlane.cs

//taken from http://answers.unity3d.com/questions/1097270/project-a-vector3-onto-a-plane-orthographically.html
//You simply project your vector onto the normal and subtract the result from your original vector. That will give you the projected vector on the plane. If you want to project a point to a plane you first need to calculate the relative vector from a point on that plane.

 Vector3 planeOrigin;
 Vector3 planeNormal;
 Vector3 point;
 
 Vector3 v = point - planeOrigin;
 Vector3 d = Vector3.Project(v, planeNormal.normalized);
 Vector3 projectedPoint = point - d;