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    <blockquote> <p>when I move the marker across the table the Y and Z axis is updated, although all I want to be updated is the Z axis, because the height of the marker doesnt change only its distance to the camera.</p> </blockquote> <p>Only true when your camera's view direction is aligned with your Y axis (or Z axis). If the camera is not aligned with Y, it means the transform will apply a rotation around the X axis, hence modifying both the Y and Z coordinates of the marker.</p> <blockquote> <p>So my guess is I need a Transformation Matrix with which I multiply each point so that I have a new coordinate System which lies orthogonal on the table surface.</p> </blockquote> <p>Yes it is. After that, you will have 2 transforms:</p> <ol> <li>T_table to express marker's coordinates in the table referential,</li> <li>T_camera to express table coordinates in the camera referential.</li> </ol> <p>Finding T_camera from a single 2d image is hard because there's no depth information.</p> <p>This is known as the Pose problem -- it has been studied by -among others- Daniel DeMenthon. He developed a fast and robust algorithm to find the pose of an object:</p> <ul> <li>articles available on its <a href="http://www.cfar.umd.edu/~daniel/Site_2/Research.html" rel="nofollow noreferrer">research homepage</a>, section 4 "Model Based Object Pose" (and particularly "Model-Based Object Pose in 25 Lines of Code", 1995);</li> <li>code at <a href="http://www.cfar.umd.edu/~daniel/Site_2/Code.html" rel="nofollow noreferrer">the same place</a>, section "POSIT (C and Matlab)".</li> </ul> <p>Note that the OpenCv library offers an implementation of the DeMenthon's algorithm. This library also offers a convenient and easy-to-use interface to grab images from a webcam. It's worth a try: <a href="http://opencv.willowgarage.com/wiki/" rel="nofollow noreferrer">OpenCv homepage</a></p>
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    1. COHey thanks for your answer. I have successfully created a Matrix which can transform between the coordinates my webcam gives me for the marker position and my Table coordinates. But I am not quite sure where to go from here. If I just take those new points it projects the model right in front of the Camera isntead of on the Marker. If I translate it on to the marker it still updates incorrecty. The problem is it does it updates according to the reflection of the monitor, which is basically at a 90° angle to the montitor(45° to the glass panel) and not straight on the table. Any ideas?
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    2. COSorry for the 2 part comment :) So it updates correctly along the projected image, but I want it to update correctly along the table. I was told to transform the camera coordinate System onto the origin of the viewplane (which should be the origin of the reflected monitor origin) and then multiply the inverse camera matrix from there. This would totally neglect the matrix I created which transforms between my created coordinate System and the cameras. (The person said my table coordinates were irrelevent to the scene) I dont really fully understand it. Any help would be greatly appreciated.
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    3. COThis is an almost one-month late reply, sorry for that. Anyway I am not quite sure what your setup is. But if what you want is only marker's coordinates in the camera referential, either apply the Pose algorithm on the marker or use 2 webcams to triangulate the position of the marker (in both cases, you will need to find known and recognizable points on your marker and in both cases you won't need the table).
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