Game Development Reference
In-Depth Information
Just as a puppet can be controlled with rods, so too can a CGI
character. The upper body capture device uses one axis of rotation at the
collar, three at the shoulder, one at the elbow, three at the wrist, three at
the base of the spine and three at the neck. Since we have two arms the
following hierarchy is created:
Hips
Torso (three potentiometers)
Left Shoulder (one potentiometer)
Left Bicep (three potentiometers)
Left Forearm (one potentiometer)
Left Wrist (three potentiometers)
Right Shoulder (one potentiometer)
Right Bicep (three potentiometers)
Right Forearm (one potentiometer)
Right Wrist (three potentiometers)
A total of 19 potentiometers. A simple
eight-channel A/D converter can be multi-
plexed to scan 32 channels if we use a
simple 4-to-1 selector. Such a selector is
fed by the PC using two output lines. The
output lines select one of four inputs to the
A/D converter. By using three four-input
multiplexers we can choose any of the
input channels. Creating the suit requires
a little engineering skill. The most com-
plex part is creating a joint with three
potentiometers. Figure 12.7 shows an
arrangement that has proven to work
effectively.
Once you have created the upper body
input device illustrated and connected the
electronics, you will need to set each
channel to the appropriate scale values.
First, you will need a simple application
program that can input a segmented
character that is divided into the same
hierarchy as the upper body input device.
For each segment you will need to record
the voltage derived from the A/D con-
verter at extremes of rotation.
Figure 12.6 A simple upper
body capture device.
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