A Brief Tutorial
Reverse Engineering &
Three-dimesional Scanning

This has come about over the last fifteen or more years due to the intense parallel development of many different types of three dimensional digitizing devices, and the powerful reverse engineering software that allows the data they produce to be manipulated into a useful form.

There are two parts to any reverse engineering application: scanning and data manipulation. Scanning, also called digitizing, is the process of gathering the requisite data from an object. Many different technologies are used to collect three dimensional data. They range from mechanical and very slow, to radiation-based and highly-automated. Each technology has its advantages and disadvantages, and their applications and specifications overlap. What eventually comes out of each of these data collection devices, however, is a description of the physical object in three-dimensional space called a point cloud.

Point cloud data typically define numerous points on the surface of the object in terms of x,y, and z coordinates. At each x,y,z coordinate in the data where there is a point, there is a surface coordinate of the original object. However, some scanners, such as those based on X-rays, can see inside an object. In that case, the point cloud also defines interior locations of the object, and may also describe its density.

Typical RE Applications
Creating data to refurbish or manufacture a part for which there is no CAD data, or for which the data has become obsolete or lost. Inspection and/or Quality Control - Comparing a fabricated part to its CAD description or to a standard item. Creating 3D data from a model or sculpture for animation in games and movies.	Creating 3D data from an individual, model or sculpture for creating, scaling or reproducing artwork. Documentation and/or measurement of cultural objects or artifacts in archaeology, paleontology and other scientific fields. Fitting clothing or footwear to individuals and determining the anthropometry of a population	Generating data to create dental or surgical prosthetics, tissue-engineered body parts, or for surgical planning. Documentation and reproduction of crime scenes. Architectural and construction documentation and measurement.

There is usually far too much data in the point cloud collected from the scanner or digitizer, and some of it may be unwanted noise. Without further processing, the data isn’t in a form that can be used by downstream applications such as CAD/CAM software or in rapid prototyping. Reverse engineering software is used to edit the point cloud data, establish the interconnectedness of the points in the cloud, and translate it into useful formats such as surface models or STL files. It also allows several different scans of an object to be melded together so that the data describing the object can be defined completely from all sides and directions.

Usually, the shortest part of any RE task is scanning or data collection. While there are exceptions, scanning might only require a few seconds or a few minutes. On the other hand, manipulating the data can be quite time-consuming and labor-intensive. It may even require days to complete this part of the job. The situation is analogous to scanning two-dimensional printed or photographic materials. It doesn’t usually take very long to scan a picture or a diagram - but getting that picture into a presentable form can be quite a lot of work, indeed.

Not all applications are created equal. Engineering is more exacting than creating a 3D model for a movie, for example. If you need to ascertain dimensions precisely, more care and diligence must be used and measurement error quantified. But accuracy and fidelity requirements are not limited to engineering. Many artistic and architectural applications also have substantial accuracy requirements. After all, would the data set that defines Michaelangelo’s David be worth anything if it was inaccurate? In some respects, aesthetic applications can be more challenging than engineering. While there may not be as great a need for absolute dimensional precision, requirements for the reproduction of surface qualities, or acquiring data from difficult subjects such as hair, represent a considerable challenge.

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RE Brief Tutorial Navigation
Scanning Technologies at a Glance      Mechanical Touch-probe Systems      Laser-based Systems      Structured-light or Broadband-source Systems      Seeing Inside - Internal Viewing Technologies RE Technology Comparison Chart	3D Metrology Systems for Manufacturing Scanners for Very Large Objects and Surveying Applications Commercial Manufacturers Directory