3D Imaging Technology:
A look at current applications in the field of cultural heritage preservation
As 3D imaging becomes more ubiquitous, its applications in cultural heritage preservation continue to proliferate. While 3D imaging does not replace other preservation technologies and techniques completely, it provides new possibilities. Not only can 3D imaging aid in documentation, research and replication for professional use, but it also creates new educational opportunities for the patrons of cultural heritage institutions. According to Wahiowiak & Karas (2009), “In a North American context, 3D scanning of cultural material continues to be new and largely uncharted territory”; however, “the success of 3D scanning projects has resulted in the recent expansion of commercial 3D technology designed with an eye to heritage applications” (p. 143). This makes it an exciting and largely experimental time for cultural heritage institutions, who are now discovering the limits and capabilities of this technology.
Overview of the Technology:
3D imaging works in two basic parts: the 3D scanner, which scans the original object and produces a 3D image, and the 3D printer, which uses that image to create a replica. The design of 3D scanners is quite straightforward. Most scanners are portable and positioned on tripods, and work much like a triangulation system. This consists of a projector and camera which sit at a fixed distance. For heritage work, lasers and white light are the most popular scanners due to their “lower cost, accuracy, and reliability” (Wahiowak & Karas, 2009, p. 148). In structured light scanning, patterns (i.e., grids, dots, lights) are projected over the surface of the object while the camera records any changes in the patterns as they move across the object’s topography. Software analyses the recorded information and produces an image as a result. These scanners are also capable of capturing color, but they do have limitations. “Objects that have deep undercuts, highly reflective surfaces, or significant subsurface scattering (like marble or jade), are difficult to scan with triangulation scanners” (Wahiowak & Karas, 2009, p. 148.)
Similarly, laser scanners project a low intensity laser point or line onto the object and the camera records the reflection back to the scanner. They must also be in a fixed position. All non-contact scanners can be disrupted by reflective surfaces like metal, very dark, light absorbing surfaces, sharp edges, translucent materials such as glass, and more malleable objects, such as fabric or feathers. Lighting can also play a significant role, particularly when attempting to capture accurate color. (Wahiowak & Karas, 2009, p. 148-151)
There are a couple ways a 3D printer may replicate an object from these scanned 3D images. One way is termed SLA (stereolithography apparatus), and it reproduces the object in an additive way. The software divides the object into thin layers and creates supports to stabilize the replica during construction that may be removed by hand later. The replica is then built layer-by-layer from the bottom up in a vat of resin. Each layer is cured by a beam of light moving over the surface. The platform under the replica then lowers beneath the surface of the resin so that the next layer may be built. Any uncured, leftover resin is washed away by hand. The process can take several hours, or even beyond a day, with large or particularly complex objects. The process is also limited by the size of the object compared to the vat of resin, as well as the weight of the object compared to what the platform can hold. And, not many devices now can mimic the natural color of the original object, so the replica will be the same color as the resin. However, the results can be extremely accurate and produced quickly without the use of molds that often damage the original object. (Wahiowak & Karas, 2009, p. 144-145)
Another method, termed CNC (computer numerical control), is a subtractive method which employs the controlled use of a cutting machine. In conjunction with software, a specialized operator determines the cuts to be made, and the machine cuts away pieces of the chosen material until the replica is complete. The machine can reposition itself on its own, but sometimes requires manual repositioning. The accuracy of the replica is “determined by the edge radius of the last cutter used” (Wahiowak & Karas, 2009, p. 146). The chosen material will also affect the outcome, and as with SLA, color is not a part of this process. (Wahiowak & Karas, 2009, p. 144-145).
When choosing a 3D imaging system for cultural heritage work, institutions must weigh the capabilities of the technology with the high standards of documentation necessary in their work. Wahiowak & Karas (2009), suggest several evaluative criteria and considerations for selection, including: accuracy, range, and resolution, field of view, speed, registration/alignment of data, imaging cameras, ease of transportation, power supply, and scanning software (p. 151-153). Appropriately advanced computers are also necessary to take full advantage of the technology. One criteria which they fail to include is cost. Although 3D imaging has become more affordable as it is adopted and more widely used in many fields, it is still expensive. Systems usually used by cultural heritage institutions which are considered more affordable still range from $100,000-$200,000 (Wahiowak & Karas, 2009, 148).
*To be continued next Topical Tuesday
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