how to transform 4 points to an xna matrix

I want to develop my own AR-Library in C#. My problem is: I have the 4 corner points of my marker and want to show 3D cube开发者_运维百科s on the marker (it's a multi-marker lib), but I don't know how to get the matrices for xna.

The term you are looking for is called "3d pose estimation". Have a look at this link: http://www.aforgenet.com/articles/posit/ . It describes the POSIT algorithm and there's also a sample application including source code you can download. Conveniently for you, it's also written in C#.

This video shows how to translate a point touched on the screen to a point in an XNA matrix:

http://bit.ly/WPARBasic

You may also be interested in the SLARToolkit for Windows Phone:

http://slartoolkit.codeplex.com/

And the Geo AR Toolkit for Windows Phone:

http://gart.codeplex.com/

They all show how to take locations on the screen or in the real world and convert them to XNA matricies.