The Stanford Large Statue Scanner

Photographs and text by Marc Levoy
November 27, 1998

On Thanksgiving Day, our graphics laboratory in the Palazzo Bargagli-Petrucci was graced by the arrival of our main scanner. This device, custom-built for us by Cyberware Inc. of Monterey, has been designed expressly for the digitization of large statues. It consists of a 8-foot vertical truss, a 3-foot horizontal arm that translates vertically on the truss, a pan-tilt head that translates horizontally on the arm, and a scanner head (described below). The entire assembly rests on a rolling base. It is shown in the process of scanning our test statue, a resin copy of an Italian statue called the Angel of Light.

Here is another view of the gantry in the process of scanning our angel. To maximize flexibility, the pan-tilt assembly can be mounted atop or below the horizontal arm, and it can be turned to face virtually in any direction. To facilitate scanning deep crevices, e.g. folds in drapery, the scanner head can also be rolled 90 degrees from its current vertical configuration to a horizontal configuration in which the green word Cyberware would appear upright. The usual standoff from the gantry to a statue is about 3 feet. To further protect statues from contact with the gantry, there is an elaborate system of automatic motion shutoffs and interlocks. Finally, the entire scanner head and pan-tilt assembly are encased in foam rubber.

The scanner head consists of a laser, a range camera, a fiber-optic white light source, and a high-resolution color camera. The laser and range camera permit digitization of 3D points with a depth resolution of 0.1mm, a typical sample spacing of 0.29mm, and a standoff of 112cm. This resolution is sufficient to accurately capture chisel marks. The working volume is 1.1m wide by 7.6m high. The light source and color camera permit measurement of surface color with a pixel size of 0.125mm over the same working volume. To reduce vibration, the pan and tilt motions employ precision ball-screw drives. To reduce deflection of the gantry during these motions, the centers of rotation and the centers of mass are made to coincide. To reduce deflection of the gantry during horizontal motion, any translation of the pan-tilt assembly in one direction is counterbalanced by translation in the opposite direction of a lead counterweight that slides inside the horizontal arm.

Here are some of the ancillary components. In the center front are two non-motorized truss extensions. These mount between the base and the vertical truss, adding 2' or 4' to the height of the gantry. At the right front is a lightweight non-motorized truss extension. It mounts between the horizontal arm and the black shelf that rides up and down on the vertical truss, adding another 8' to the height of the assembly. Combining the scanner head, all the extensions, the base, and a second platform not shown here, creates a gantry that can reach 24' - the height of Michelangelo's David on its pedestal. (The use of the 2' and 4' extension together, and the height provided by the second platform, became necessary when we discovered that the statue was 3 feet taller than we thought it was.) To prevent tipover in its maximum configuration, weights are fitted into receptacles in the base. At left front is a mobile electronics cabinet that will travel with us to the museums. Scanning is scheduled to begin in January.

Here is a labeled collage of these photographs. Indicated in orange on the collage are the four degrees of motorized freedom of the gantry

Credits

Cyberware: Duane Fulk (project leader & principal designer), Everett Reed (optics), Jim Meek (electronics), Lloyd Addleman (engineering), David Addleman (software), Bill Eden. John Gianelli, Alex Kamimori, Brian King, Mick McGuire, Cesar Puga, Jeannie Sherry, Jose Velasquez.

Stanford University: Marc Levoy (project leader), Brian Curless (design), Kari Pulli (software lead), Jeremy Ginsberg, Matt Ginzton, David Koller Lucas Pereira, Szymon Rusinkiewicz.

webmaster@graphics.stanford.firenze.it

	On Thanksgiving Day, our graphics laboratory in the Palazzo Bargagli-Petrucci was graced by the arrival of our main scanner. This device, custom-built for us by Cyberware Inc. of Monterey, has been designed expressly for the digitization of large statues. It consists of a 8-foot vertical truss, a 3-foot horizontal arm that translates vertically on the truss, a pan-tilt head that translates horizontally on the arm, and a scanner head (described below). The entire assembly rests on a rolling base. It is shown in the process of scanning our test statue, a resin copy of an Italian statue called the Angel of Light.
	Here is another view of the gantry in the process of scanning our angel. To maximize flexibility, the pan-tilt assembly can be mounted atop or below the horizontal arm, and it can be turned to face virtually in any direction. To facilitate scanning deep crevices, e.g. folds in drapery, the scanner head can also be rolled 90 degrees from its current vertical configuration to a horizontal configuration in which the green word Cyberware would appear upright. The usual standoff from the gantry to a statue is about 3 feet. To further protect statues from contact with the gantry, there is an elaborate system of automatic motion shutoffs and interlocks. Finally, the entire scanner head and pan-tilt assembly are encased in foam rubber.
	The scanner head consists of a laser, a range camera, a fiber-optic white light source, and a high-resolution color camera. The laser and range camera permit digitization of 3D points with a depth resolution of 0.1mm, a typical sample spacing of 0.29mm, and a standoff of 112cm. This resolution is sufficient to accurately capture chisel marks. The working volume is 1.1m wide by 7.6m high. The light source and color camera permit measurement of surface color with a pixel size of 0.125mm over the same working volume. To reduce vibration, the pan and tilt motions employ precision ball-screw drives. To reduce deflection of the gantry during these motions, the centers of rotation and the centers of mass are made to coincide. To reduce deflection of the gantry during horizontal motion, any translation of the pan-tilt assembly in one direction is counterbalanced by translation in the opposite direction of a lead counterweight that slides inside the horizontal arm.
	Here are some of the ancillary components. In the center front are two non-motorized truss extensions. These mount between the base and the vertical truss, adding 2' or 4' to the height of the gantry. At the right front is a lightweight non-motorized truss extension. It mounts between the horizontal arm and the black shelf that rides up and down on the vertical truss, adding another 8' to the height of the assembly. Combining the scanner head, all the extensions, the base, and a second platform not shown here, creates a gantry that can reach 24' - the height of Michelangelo's David on its pedestal. (The use of the 2' and 4' extension together, and the height provided by the second platform, became necessary when we discovered that the statue was 3 feet taller than we thought it was.) To prevent tipover in its maximum configuration, weights are fitted into receptacles in the base. At left front is a mobile electronics cabinet that will travel with us to the museums. Scanning is scheduled to begin in January.
	Here is a labeled collage of these photographs. Indicated in orange on the collage are the four degrees of motorized freedom of the gantry