| OCR Text |
Show 80 edges and at silhouette edges of the patch. These oints should then be kept sorted according to their screen X coordinate to ease this next step. Yv2 Xuu - 2 Yu Yv Xuv + Yu2 Xvv > 0 The points in the edge list fall into two categories. Those on the left side of the patch and those on the right side. The "left" edges trigger the creation of intersection points when they are passed by the scan ray, the "right" edges signal the removal of intersection points. Left edges are characterized by Xu>O:u=O or Xu<O:u=l etc. for boundary edges and (as will be shown below) for silhouette edges. Right edges are characterized by similar expressions with the signs reversed. When the X scan beam passes a left boundary edge, one new active intersection must be created. The initial guess for the U,v position of this point can be the same as the u,v of the boundary edge. The bivariate iteration step for the next picture element location will adjust it to its exact position. This is shown in figure 20. When the beam passes a left silhouette edge, two new intersection points must be created, the one on the front side and the one on the back side. The initial guesses for the locations of these points cannot be the position of the silhouette tracker since this is an extremum of the patch in |
