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Large Volume and Random Access 3D Laser Scanner

The Large Volume 3D Laser Scanner (Figure 1a) is a dual axis scanning system designed for high-resolution monochrome 3D digitization of large objects and structures.

For museum and heritage applications, the system has been used to record archaeological sites in Israel, as well as for digitizing large sculptures at the Canadian Museum of Civilization. Although the Large Volume Laser Scanner is currently a research prototype system in our laboratory and is not commercially available for heritage applications, a commercial space flight version was constructed by Neptec (http://www.neptec.com) for space flights in 2001 and in 2005.

Principle of operation:
The basic optical configuration for the system is depicted in Figure 1b. The x-axis scanner achieves the auto-synchronized scanning, while the y-axis scanner provides deflection of both the projected and the detected beam. Both mirrors are driven by galvanometers. This configuration enables two imaging modes. For raster mode imaging, the x-axis scanner (fast axis) is used for the line scanning while the y-axis (slower speed) vertically deflects the scanned beam to produce a raster image. For panoramic scan mode imaging, the x-axis scanner is used for vertical scans while the scanner is rotated on a motorized pan and tilt stage to record panoramic views of the scene. In operation, the scanner can be mounted either on a conventional photographic tripod (Figure 1c) or on a custom designed telescoping tripod, which can be raised to a height of 10 m (Figure 1d).

The system allows 3D recordings at a scanner to object distance (scanner standoff) which ranges from 50 cm to 10 m. At a standoff of 50 cm, it provides a resolution of 70 microns (0.07 mm), which increases as the square of the distance. For example, at a 10 m standoff, the resolution is 10 mm. Spatial sampling resolution along the x and y scan directions is determined by the laser beam diffraction limit as discussed above. Theoretical predictions and laboratory measurements have shown that images with a dimension of more than 10,000 x 10,000 pixels are possible. This spatial resolution combined with a z measurement uncertainty of better than 0.1 mm at close range yield very high-resolution images.

Figure 1: Components and Configuration of the Large Volume of View 3D Laser Scanner

Figure 1: Components and Configuration of the Large Volume of View 3D Laser Scanner
(a) The Large Volume 3D Laser Scanner mounted on pan and tilt unit. The system includes a video camera to facilitate remote positioning of the scanner. (b) Schematic optical configuration of the dual axis scanner. (c) The scanner is mounted on a conventional tripod to scan archaeological site features at Caesarea in Israel. (d) The scanner is mounted on a telescoping tripod to scan the sculpture Mythic Messengers at the Canadian Museum of Civilization. The sculpture is mounted 4 m above ground on an exterior wall and measures 9 m long x 1.2 m