Tham khảo tài liệu 'active visual inference of surface shape - roberto cipolla part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 4 Qualitative Shape from Images of Surface Curves Introduction Imagine we have several views of a curve lying on a surface. If the motion between the views and the camera calibration are known then in principle it is possible to reconstruct this space curve from its projections. It is also possible in principle to determine the curve s tangent and curvature. In practice this might require the precise calibration of the epipolar geometry and sub-pixel accuracy for edge localisation and or integrating information over many views in order to reduce discretisation errors. However even if perfect reconstruction could be achieved the end result would only be a space curve. This delimits the surface but places only a weak constraint on the surface orientation and shape along the curve via the visibility and tangent constraints - see later . Ideally rather than simply a space curve we would like a surface strip 122 along which we know the surface orientation. Better still would be knowledge of how the surface normal varied not only along the curve but also in arbitrary directions away from the curve. This determines the principal curvatures and direction of the principal axes along the strip. This information is sufficient to completely specify the surface shape locally. Knowledge of this type helps to infer surface behaviour away from the curves and thus enables grouping of the curves into coherent surfaces. For certain surface curves and tracked points the information content is not so bleak. It was shown in Chapter 2 that the surface normal is known along the apparent contour the image of the points where the viewing direction lies in the tangent plane 17 . Further the curvature of the apparent contour in a single view determines the sign of the Gaussian curvature of the surface projecting to the contour 120 36 . From the deformation of the apparent contour under viewer motion a surface patch first and second fundamental forms can be recovered 85 27 . The .
