Find points inside 3D polygon

There matrix P with coordinates XYZ points. (~ 30-40 points ) There is a matrix Q in which the coordinates of the points are the vertices of a plane. (4 points - a rectangular cross section )

It is necessary to leave only those points of the matrix P, which lie within the plane Q. The three-dimensional region . inpolygon not suitable.

Help please .

[John Mahoney]

Hi Timofey, A generic point in 3D will not lie within a given plane. Can you clarify?

Do you:

- happen to know that your points in 3D are also within the infinite plane defined by Q, but you want the subset that lies within the prescribed rectangle?

- not know anything special about the points in 3D, but want those that might happen to be precisely within the infinite plane Q?

- not know anything special about the points in 3D, but want those that are "close enough" to the infinite plane Q?