Cadalyst - January/February 2009 - (Page 16) techtrends From Point Clouds to Physical Parts Because the point-cloud data acquired by an HDS scanner can be converted into CAD objects, it also can be reproduced (after some cleanup) in STL format, accepted by 3D printers. Geoff Jacobs, senior vicepresident of strategic marketing for Leica Geosystems HDS, proposed two options: Create a model in Cyclone and export via COE (Cyclone Object Exchange) format to AutoCAD for conversion to STL format, or use CloudWorx to create the model from the point clouds directly in AutoCAD for export in STL format. For owners and operators of historic sites such as Nenagh Castle, the 3D-printed model could serve not only as an archival physical copy (possibly for display during periods when restoration work makes the site inaccessible to the public) but also as a marketable souvenir in their gift shops. Figure 2. Realigning the point-cloud data into one continuous surface, Gridpoint Solutions’ partners produced this 2D elevation view of the castle. The stonework is not textured but meticulously traced — one piece at a time — to give an accurate accounting of the makeup of the façade. preserving, and maintaining access to records that form part of Northern Ireland’s unique cultural heritage.” The task traditionally was done on paper, but PRONI points out, “Northern Ireland Civil Service and wider public-sector business needs have changed and, in order to support that change, PRONI has to be in a position to provide a digital archiving service.” How to Flatten a Castle One summer day, when the highland weather was ideal for scanning, Graham climbed with the 37-lb HDS scanner to the walled site where Nenagh Castle is located. (Graham and other HDS users would be glad to know that nextgeneration equipment is lighter. Geoff Jacobs, senior vicepresident of strategic marketing for Leica Geosystems HDS, pointed out that the HDS6000 weighs 30 lb.) To remain consistent with its own established archival protocols, the OPW requested that one of the deliverables be an unwrapped (or flattened) 2D elevation view of the castle. “No problem,” Graham told the OPW officials. He thought he could find a special button or a command in the software to convert the point-cloud data of the semicylindrical shape into a flat surface. Eventually, he discovered that the function he wanted didn’t exist on the scanner’s software menu. He would have to manually slice the point-cloud data into vertical strips and realign them into one continuous flat surface. But the structure had very little architectural variation. It was stonework all around, making it incredibly difficult to discern where each strip should begin and end. That’s where Bishop Flannery — or, rather, the windows he installed in the 1860s — came to Graham’s rescue. 16 “We did about six or seven scanning sessions from different vantage points,” explained Graham. “We registered our [scanner] fields of view to one continuous point cloud, then used features on the tower [which were, in fact, the windows in Flannery’s 1860 battlements] to identify and align the different strips of point clouds to be passed to the CAD technician.” Graham explained that to do the same project using photogrammetry (an option the OPW explored before settling on HDS) would require placing targets on the castle wall, a process that could lead to drilling and attaching semi-permanent fixtures in the castle surface. Because the castle is a heritage site, getting the necessary permits and approvals to do anything drastic on its surface would take time. Traditional surveying methods — taking physical measurements of the structure to create as-built drawings of the castle — would have required the use of scaffolding, a more time-consuming process that comes with safety concerns. By contrast, Graham spent only a day at the site, capturing the point clouds that make up the complete, detailed shape of the castle from a distance. Onsite and Offsite Work Unwrapping the point clouds was just one part of the client’s requirements. The next step called for reproducing a stone-by-stone accounting of the castle’s tower, or façade, to be printed on special archival paper for posterity (figure 2). So Graham partnered with a local archeology consultancy, Farrimond MacManus, to trace the stonework — one piece at a time — discernible in the point-cloud density. It’s a process that took about four months to complete. But, with the data accessible from a local hard drive, the www.cadalyst.com cadalyst January/February 2009 http://www.cadalyst.com
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