Tham khảo tài liệu 'active visual inference of surface shape - roberto cipolla part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 96 Chap. 4. Qualitative Shape from Images of Surface Curves Figure The visibility constraint. a The visibility constraint restricts the surface normal n to lie on a hemisphere of the Gauss map Gaussian sphere b By intersecting these constraint regions for known viewer motions a tighter constraint is placed on the normal. Figure The tangency constraint. a The tangent constraint restricts the surface normal to lie on a great circle of the Gaussian sphere b By intersecting this curve with the constraint patch from the visibility constraint the surface normal is further restricted to an arc of a great circle. . Surface geometry 97 sphere places a tighter constraint on n figure . Clearly motion which rotates by 180 about the object determines the surface normal provided of course the point is always visible. The point will not be visible if another part of the surface occludes it or if it has reached the extremal boundary the back projection of the apparent contour in the image . However when it reaches the extremal boundary the normal is fully determined 17 . The viewer motion must be accurately known in order to fully utilise the visibility constraint over a sequence of views. Uncertainty in motion could be included in a primitive fashion by intersecting regions larger than a hemisphere. The excess over a hemisphere would be bounded by estimates of error in viewer motion. The constraint on the normal provided by the visibility constraint is applicable to texture points as well as smooth curves. The following constraint exploits the continuity of the curve. Tangency constraint The space curve tangent lies in the surface tangent plane and this constrains the surface normal n 0. This orthogonality condition generates a constraint curve which is a great circle on the Gaussian sphere figure 23 . If the curve tangent could be determined exactly then intersecting the great circle with the constraint patch from the visibility constraint .
