CS CS 175 – Week 2 Processing Point Clouds Registration

CS Overview registration of multiple scans

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

CS 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

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

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

CS 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

CS 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

CS Registration ICP (iterative closest points) find point pairs compute best transform apply transform iterate until numerical convergence

CS 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

CS Registration ICP variants point selection point matching weighting error metric point-to-point point-to-plane