Geometric methods for 3D shape understanding and reconstruction Helmut Pottmann Vienna University of Technology Geometry provides a rich source of knowledge and methods for understanding and reconstructing 3D shapes from measurement data. We will illustrate this at hand of line geometry and Laguerre geometry. Line geometric methods are applied to the system of estimated surface normals at data points, whereas the Laguerre geometric approach addresses estimated tangent planes at data points. The combination of classical geometric results with tools from scientific computing yields algorithms for the detection and reconstruction of special surfaces such as rotational and helical surfaces, ruled surfaces, developable surfaces (including general cylinders and cones) and canal surfaces. We address various industrial applications and outline directions for future research.