1. CS175 2003 1 CS 175 – Week 2 Processing Point Clouds Registration

2. CS175 2003 2 Overview registration of multiple scans

3. CS175 2003 3 Registration each scan consists of camera position viewing direction grid of distances also called “range image” yields “standard” triangulation

4. CS175 2003 4 Registration conversion to 3d point cloud choose local coordinate system origin = camera position x-axis = “horizon” y-axis = viewing direction z-axis = perpendicular to x and y

5. CS175 2003 5 Registration standard triangulation 0, 1, or 2 triangles per quad choose shortest diagonal make triangle if edges not too long

6. CS175 2003 6 Registration combine two scans find rigid body transform between local coordinate systems translation and rotation track position and viewing direction compute! transform points

7. CS175 2003 7 Registration compute best rigid body transform need overlapping region point pairs closest point from point cloud closest point in triangulation minimize overall distance between point pairs

8. CS175 2003 8 Registration combine multiple scans analogy to physical system dynamical system of rigid bodies distances = spring forces find minimum of potential energy e.g. Euler method

9. CS175 2003 9 Registration ICP (iterative closest points) find point pairs compute best transform apply transform iterate until numerical convergence

10. CS175 2003 10 Registration properties of ICP convergence guaranteed local minimum needs good initial value track position and direction best rigid body transform for manually selected point pairs manual coarse alignment

11. CS175 2003 11 Registration ICP variants point selection point matching weighting error metric point-to-point point-to-plane