This type of problem is called “unprojection”, “ray casting”, or “picking”. Googling for those terms will probably provide you some useful links.

The basic idea is to use the mouse click position to generate a ray in the 3D world space. It will start at the camera and pass through the pixel you clicked. Then you find where the ray intersects the scene. In your case you’d do a ray-plane intersection with the ground plane, and use the coordinates of the intersection point to tell which tile was clicked.

http://www.gamedev.net/topic/636063-help-calculating-this/

Hi guys ,

Please check the above link . I don’t know how to post images here . Any one know how to calculate this and solve this issuel.Thanks in advance.

john lin