Cadalyst - May 2008 - (Page 34)

industrytrends There usually is too much data in the point cloud collected from a scanner/digitizer, and some of it will be unwanted noise. Without further processing, the data cannot be used by downstream applications, such as CAD/CAM software or in rapid prototyping. RE software is used to edit point-cloud data, establish the connections of the cloud points, and translate it into useful formats, including surface and solid models or STL files. It also combines several different scans of an object so that the data describing the object can be defined completely from all sides. Scanning Methods Several digitizing technologies are available today. They include contacting/feature-based (mechanical touch probe) and noncontacting (laser-based) instruments and hybrid systems. Feature-based scanning systems. Feature-based scanning is a method by which features of an object are scanned by physical contact. A mechanical touch probe, also known as a contacting digitizer, is a physicalpart contact device and method well suited for prismatic parts, such as an automotive transmission housing. The touch probe is a device that is connected to a computer and lets you know when and where in space contact is made with an object (figure 1, p. 32). Disadvantages of contacting devices include the fact that they can distort soft objects. Additionally, they can be too slow for digitizing organically shaped parts because they usually require too much time and labor for scanning complex curved surfaces (although there are workarounds for this, such as scribbling a complex surface with the touch probe). On the other hand, such devices are not affected by the color, transparency, or reflectivity of a surface the way laser and other light-based systems can be. And while they can be relatively slow, contacting devices are often the fastest way to digitize simple surfaces for which just a relatively few data points are required. Because feature-based scanning actually captures features on the fly, the resulting data is both native and feature based, so surFigure 2. Laser scanning is well suited for capturing freeform shapes and soft face and solid-model features can be derived objects with a high degree of accuracy. directly from the scan. Point-cloud scanning systems. Pointcloud scanning is performed using a laser What eventually results from each of the data-collecscanner that is a physical-part noncontact device. The tion methods is a description of the physical object in 3D space called a point cloud. Point-cloud data typically defines method is well suited for organic, freeform, artistic parts, such as statues. It is also well suited to scanning soft objects points on the surface of a scanned object in terms of x, y, with surfaces that might be distorted by a touch probe. z coordinates. At each x, y, z coordinate in the data where Point-cloud scanning is not well suited, however, for pristhere is a point, there is an associated surface coordinate of the original object. 34 www.cadalyst.com cadalyst May 2008 http://www.cadalyst.com

Table of Contents Feed for the Digital Edition of Cadalyst - May 2008

Cadalyst - May 2008 Contents Editor's Window Cad Central A Solid Job in AutoCAD Today’s Power — Quad-Core Workstations Performance — Tomorrow’s Possibilities Reverse Engineering an Antique Italian Treasure Trends in Reverse Engineering NextEngine 3D Scanner — Reverse-Engineering Tool Setting CAD Standards Fight for Your Hardware Rights The Jack and Jill of Ergonomics Technology for Civil Infrastructure Cad Cartoon Issue Indexes Shortcuts and Solutions

Cadalyst - May 2008

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