Computer Aided Engineering Design

296 COMPUTER AIDED ENGINEERING DESIGN

Kinematics can be extracted using the skeletal data while cosmetic design can be accomplished
using the outer form. For custom design of both limbs, heuristic design based on the existing data
bank may be suggested and incorporated. An orthopedic may prefer stress simulation to foresee
the effects of a range of loads, say during gait, on joints and links for which the reverse engineered
CAD model shall be useful.
(c) Three dimensional models of internal organs can enhance a surgeon’s pre-operative planning,
especially in life saving situations involving a single procedure. Point cloud data generated from
the biological form is used for its shape synthesis.
(d) An artist/archeologist can also benefit from reverse engineering. Archeologists can reconstruct
fossils, archaeological collections from fragmentary material to view and analyze more accurately
without damaging the original artifact. They can even reproduce artifacts in absence of the
original object by creating 3-D model archives. Artists/sculptors can reproduce their creations in
the original form for a larger customer base.
(e) Graphics and multimedia personnel can create enhanced quality computer models of comic/real
life creations for animation, movie, virtual reality and show renderings from physical models.
(f) A city planner/geologist can model terrain surfaces for analysis and presentation. The availability
of three-dimensional computer models enhances better planning of civil infrastructure based on
terrain characteristics with minimal requirement of terrain modification.

The above list provides only a glimpse of the application domain of surface/solid modeling from
point samples. The availability of a variety of digitizing equipments and spectrum of software has
expanded the application of reverse engineering to almost every area where 3-D modeling of free-
form shapes may play a significant role. The procedure to acquire shape information in discrete form
to build geometric models depends on the type of the physical object and the purpose for which the
model is being created.

10.2 Point Cloud Acquisition

A broad classification and listing of different methods for acquiring point cloud data is given in
Figure 10.1. Each method uses some mechanism or phenomenon for interacting with the surface or
volume of the object of interest. Non-contact methods use light, sound or magnetic fields while in
tactile or contact methods, the surface is probed mechanically. In each case, appropriate analysis of
the data acquired has to be performed to locate the positions of points on the surface. For example,
in laser range finders, the time of flight is used to determine the distance traveled and subsequently
the point location. Each method has pros and cons, which require that the data acquisition system
should be carefully chosen for shape capturing.

Figure 10.1 Data acquisition methods

Data acquisition

Non-contact methods

Optical

Triangulation

Interferometry

Image analysis

Ranging

Structured

Acoustic Magnetic Robotic arms

Coordinate measuring machine

Tactile methods