title: Photogrammetry, Width and height ratio of rectangle in image
body: <p>How do I get the width and height ratio of a sheet of paper (or some other rectangular thing) from an image? Here is an example/image that maybe makes my question a bit clearer, <a href="http://imgur.com/Hcu0CNi" rel="nofollow">http://imgur.com/Hcu0CNi</a> . I know the coordinates of the corners of the paper in the image. I guess it is impossible to get the true width and height of the paper, but it should be possible to get the width and height ratio of the paper, right?</p>