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I'm currently working on grasping cuboid objects (aka small cardboard boxes) that are placed on a table with a robot that has a camera attached to its gripper. I need the exact size of the box (error ~ 1mm) and its position on the box. I have some ideas but I also would like to hear some other approaches before I really start implementing.

Some additional info:

  • The boxes are textured, although the edges are commonly white to they don't appear good in the edge image.

  • I could change the surface, the objects are placed on, so that I could use some kind of pattern to simplify the segmentation process or even use a electro-luminous foils to have perfect edges (at the boundary of the object).

  • I can actively move the arm (which has a good (<1 mm) odometry) so that I could take two images from different positions

My strategy so far: I take two images from known positions so that I at least can compute the height of the box. I then find the edges of the box (segmentation against the background) and use the intersections of the edges to find the corners of the box in the image. Together with the known height I can compute the size and position of the box on the table. In most cases the corners would be sufficient but there is one hard case: If I'm looking straight on the box (no sides visible), I can only detect four corners in the edge image. And in this case I can't decide if I have on short but high box or a longer flat box.

What do you think about this approach?

Or do you have a completely different idea? The gripper is still work in progress so that we could even attach new sensors.

Foo
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    Take a look at the calibration methods of opencv. You need to calibrate your camera to start a process like this. Pre-knowledge of starting point is critical. Using homograpy methods, and with some trigonometry, you can calculate real distances. If you need arm manipulation within connected joints, the maths become harder. You may need to read about inverse kinematics (check `Robot Manipulators` by R.P.Paul) – baci Jul 01 '13 at 12:18
  • Hey! The camera is of course already calibrated and I can rely on the kinematics. – Foo Jul 01 '13 at 17:07

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