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Question about Pose Estimation

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Question about Pose Estimation

Postby whc0216 » Wed Jun 18, 2014 12:58 pm


I am using AForge to do 2D marker pose estimation, and draw a graphics on the top of it, similar to AForge example:
And I have few questions while I was going through:

I am a little bit confused about when to use CoPosit, and Posit algorithm. I do understand that CoPosit works out well on Co-planar and Posit works out well on non Co-Planar. So I am using 2D Square marker, and have four corner points. I looked straight down to the maker, so I put the image points and model points:
(-160, 120) --- (-50, 0, 50)
(160, 120) --- (50, 0, 50)
(160, -120) --- (50, 0, -50)
(-160, -120) --- (-50, 0, -50)
However, using CoPosit does not give a nice result. I was expected an identity matrix or something close, but it was not. Apparently, Posit returns a result that I want. Whenever I look straight down the marker and rotate a little bit (so the marker looks like rhombus), using Posit actually works out well, compare to CoPosit, but I am not sure why though. I thought this is still in the same planar?
On the other hand, if I look at the marker with some angle (Just like an AForge example), then CoPosit works out well.
I am not sure why I have to use back and forth with Posit or CoPosit algorithm, when viewing same 2D square (Co-planar plane) in just different angle

Another question is that I am trying to draw a cube on the top of the pose estimation I received, and it somewhat draws weird.
So I used AForge sample/test application (exe files on the website), and I am not sure why the pose estimation returns y and z axis flipped?
I want to use the coordinate system where X-axis goes to the right, Y to the up, and Z to the front, and it looks like AForge has different coordinate system?
I am not sure how to change axis after the pose estimation, so that I can draw the cube properly? I tried both two results from CoPosit (CoPosit returns two, and I can use whichever works out better). Btw, I am using the result on OpenGL for drawing.

I am having this problem since last month, and can someone help me on this?
Thank you very much.
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