Chapter 10
Geometric Modeling Using
Point Clouds
Chapter 7 discussed the modeling of surfaces with regard to designing solid shapes as a collection of
closed, simply connected surface patches. When designing products with free form shapes such as the
aircraft wings and fuselage, car body and its doors, seats and windshields, the shape information has
to be acquired as a set of data points and then the surface patches have to be designed from the same.
Data points can either be user-specified for an entirely new design or can result as a large discrete set
calledpoint cloud from say laser scanning of an existing product or its prototype. Reverse engineering
alludes to constructing surface patches from the point cloud data. This chapter describes some
methods on point cloud acquisition and surface/solid modeling using the acquired data.
10.1 Reverse Engineering and its Applications
Reverse engineering is the process of creating engineering design from existing components or their
prototypes. The existing part is recreated by acquiring its surface data using a scanning or measurement
device. For a new component whose original design data is not available, a CAD model is created
using conceptual clay or wood model for further analysis and possible form changes. Coordinate
measuring machines (CMMs) have been used to extract surface data but their data capturing operation
is very slow for parts having intricate free-form surfaces. In recent years, laser scanning has become
a powerful tool in capturing the geometry of complicated models. With present and upcoming range
of sensing devices and associated software, surface modeling from point cloud samples of physical
objects is a rapidly evolving discipline. A few of the many applications of reverse engineering are
listed below.
(a) Generation of custom fits to human surfaces is plausible with reverse engineering to design
products like helmets, shoes, arm and knee guards, space suits and others. The inside hull can be
obtained by scanning the human surface (head, feet or body) while the outside hull can be
designed keeping weight, safety, aerodynamics and many other such factors in mind.
(b) Custom prosthetic design is a medical application of reverse engineering. Custom prosthetics
help in better and faster post operative recovery as well as provide better cosmetic appearance to
an amputee. In a case where an amputee has a natural limb, the point cloud data can be determined
for the skeleton and the outer form from the intact limb using X-ray and laser scanning respectively.