Machine Design

What’s the Best Way to Capture Shape Data?

Scanning technology, hardware, and software have advanced such that more and more firms can make use of digital representations of physical objects in production workflows.

Digital shape-sampling and processing (DSSP) adds value to all stages of design, from conception to mass customization.

There are different data representations at different stages of the design cycle, from physical object to CAD model. The ultimate goal is a manufactured product (not all products require each kind of data representation). A physical object, of course, has properties such as shape. A coordinate- measuring machine or an articulated arm takes digital measurements from the shape’s outer surfaces to generate a digital point cloud. Point clouds are most useful in metrology — for example, a sparse point selection can be replaced by richer color error maps to show deviation trends.

Cloud data from 3D scanners can be converted into surface data. Programs including Raindrop GeoMagic, Innovmetric, RapidForm, and AliasStudio among others, convert scanner point clouds into watertight polygonal meshes. When imported into industrial-design software or 3D CAD, these meshes can, for instance, provide close representations of the physical object for packaging development. Meshes also allow interference checking in assemblies and support aerodynamic and mold-flow studies so users can pinpoint needed design changes earlier in the cycle. Meshes also generate photorealistic images for marketing studies as well as let dispersed teams share 3D models. Finally, meshes can build forms as Class A Nurbs surfaces.

Tools for data capture range in cost from a few thousand dollars to hundreds of thousands. A complete device will include a registration method, a scanning or capturing capability, and a way to extract points into a cohesive cloud. Software that converts the cloud to a mesh eliminates typical scan problems such as removing registration marks and filling in holes. Depending on the scanning method, smoothing and reduction can help make polygonal meshes easier to work with. Finally, software that converts meshes to Nurbs might be necessary for downstream users who lack a way to work with meshes.

— Paul Deyo

Paul Deyo has over 28 years experience in transportation and industrial design, including reverse engineering, scan processing, visualization, and Class A surfacing. He is currently a product designer on the Alias team at Autodesk, focusing on modeling.

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