How can I calculate homography from the room height and camera calibration matrix?

1. How do I find a homography?
2. How to calculate homography matrix in OpenCV?
3. How many points needed for homography?

How do I find a homography?

The homography can be estimated using for instance the Direct Linear Transform (DLT) algorithm (see 1 for more information). As the object is planar, the transformation between points expressed in the object frame and projected points into the image plane expressed in the normalized camera frame is a homography.

How to calculate homography matrix in OpenCV?

How to calculate a Homography ? To calculate a homography between two images, you need to know at least 4 point correspondences between the two images. If you have more than 4 corresponding points, it is even better. OpenCV will robustly estimate a homography that best fits all corresponding points.

How many points needed for homography?

We have seen that a homography can be used to map one image to the other in the case of pure camera rotation or a planar scene. If such a homography exists between the images, four points are sufficient to specify it precisely.