[Figure 17] The Polhemus scanner is easy to use but cannot scan metal surfaces. Image courtesy of Polhemus Corp.

Polhemus
Polhemus makes a unique scanner called FastSCAN. This product can deliver quick and fairly high quality scans when the user is experienced and has some basic knowledge of the scanner's settings. The software used in this system has the remarkable capability to merge multiple passes accurately and easily. This scanner also has the distinction of being very inexpensive and easy to use compared to the Cyberware scanners. The scanner itself is a handheld wand that is passed over the object being scanned. Multiple passes randomly gathered by hand are assembled and put into accurate world-space using the magnetic calibration system (Figure 17).

This scanner calibrates itself using the Polhemus magnetic tracking system. The problem with the magnetic tracking base is that metal objects, whether motion capture, digitizing or scanning, will adversely affect any magnetic system. This wouldn't be such a big deal except that many objects have metal in them. When a design needs to be modeled and executed in full physical sculpted form prior to capturing the form for 3D modeling, the sculpture has to be specially designed without any metal armatures. In some cases, the building that houses the system adversely affects the results of the scanner.

Minolta
The Minolta VIVID line of scanners are true laser scanning apparatuses. The scanning object operates the device from a PC connected to the scanner. The object being scanned is placed in front of the scanner at a fixed distance. The scanner is then activated. In less than one second, the scanner passes a laser over the surface of the object that is visible to the scanner. Because this scanner is basically a box that sits in front of the object and cannot “see” the entire model at once, the operator needs to rotate the model to get additional views scanned. As with most scanners that require multiple passes, multiple passes need to be assembled into one continuous, clean, watertight mesh. This takes time and skill and sometimes requires an additional software package to clean up the geometry. Unlike the Polhemus FastSCAN, this scanner also captures texture mapping information, as well as 3D geometry.

[Figure 18] A scan of an actual helicopter shows how lidar can capture large data sets quickly. Image courtesy of Alan Lasky.

Lidar
A variation of laser scanning that is used almost exclusively for very large scanning applications is lidar (light detection and ranging). This type of scanner is also called a time-of-flight laser scanner. This technology was originally developed for scientific and military applications (Figure 18). It has become very useful for digitizing large structures because of its inherent ability to sample a large number of points within a short amount of time.

Lidar has been instrumental in addressing several problems related to integrating live-action photography with 3D digital imagery. Normally when the visual effects studio receives background plates for digital effects, some guesswork is involved when creating digital environments based on the background photography. Although it is usually not necessary to re-create the environment so it can be rendered photorealistically, it is normally required to build objects that will be used to cast shadows on and create objects for tracking purposes. If the lidar data is acquired correctly, it addresses many of these problems.

The person using the data, however, needs to pay careful attention to criteria associated with the acquisition of lidar data. Before approving any data that is received from a lidar capture session, the modeler responsible for using the data should make sure that the data meets the following criteria: