Kameda, Research, Documents and Info

Algorithm

In this section, we describe a contour based algorithm to estimate a pose of the articulated object. This algorithm uses the definition of the model, but does not use the values in the model so we can easily change the target object without modifying the algorithm.

Each part in the model is taken up one by one and its rotation angles are determined based on the overlap relationship between the contour of the silhouette and that of the projected region on the image plane.

Suppose a set has the parts whose rotation angles have been determined and a set has the parts whose parent part belongs to . The rest parts belong to a set . At the beginning only contains the root part and all other parts are in .

1.   Selection of the Part
   Select a Part i in . If there is no part in , the algorithm terminates. Make a new candidate-list for Part i. A candidate in the candidate-list represents a possible pose of Part i, and has at most three rotation angle values which are quantized by a certain unit interval. The unit size defines the resolution of the pose estimation. A candidate can not have values that make the projected region of Part i stray out from the silhouette. If there exist no candidates in the candidate-list, go to Step 3.
2.   Estimation of the angles
   To find the best pose of Part i, the system measures the length of the contour where the contour of the silhouette overlaps with that of the projected region for each candidate in the candidate-list. The candidate with the largest overlap is adopted as the estimated result. The rotation angles are fixed to the values of the candidate, and then it is removed from the candidate-list. Move Part i from to , and the children of Part i in are moved to . Go to Step 1.
3.   Backtracking
   Backtrack from Part i to the root part until Part j, which keeps at least one candidate in the candidate-list, is found. Move all of its children descendants into . For Part j, execute the same algorithm as Step 2. Go to Step 1.

Since it is not clear what kind of criterion is necessary to select the part in Step 1, our method here selects it arbitrarily. We are currently investigating this problem.