H. G. Dietz
Department of Electrical and Computer Engineering
Center for Visualization & Virtual Environments
University of Kentucky, Lexington, KY 40506-0046
Given that a computer is controlling the camera's capture parameters, it is only natural to think about computer control of the capture parameter that is the direction in which the camera is pointing. There are several key issues to consider in pointing control:
The range of motion control available varies widely.
Cameras that do support motion control most often incorporate a simple motorized pan/tilt mounting system. Panning refers to rotation in a horizontal plane (left/right), whereas tilting refers to rotation in a vertical plane (up/down). In fact, there are a variety of coordinate systems commonly used to describe rotations, and the pan/tilt terminology is making assumptions about the orientation of the mount which might or might not apply for a specific camera installation.
However, most cameras do not have any motion control mechanism integrated. In such a case, a motion control system can simply have one or more cameras attached. These motion control systems range from simple motorized platforms with rotation or translation control up to fully mobile robots.
Some (fairly expensive) webcams and surveilance video cameras have built-in pan/tilt mounts, but the mechanical accuracy of pointing is often very low (depending on observing the images to confirm orientation) and some simply continuously pan through a specified range (with no pointing control at all). There are quite a few video cameras incorporating mounts that use the Pelco protocols (see links below), however, the pan/tilt control interface does not appear to be well standardized for digital cameras.
Starting at less than $100, there are a wide range of pan/tilt mounts commercially available. In general, these units are intended either for security systems or for human photographers to use for remotely pointing a camera. The security-oriented systems often provide continuous sweeping motions within preset limits and some also provide speed control (allowing smoothly panning video capture).
Other types of motion control mounts that may be usable include X-Y translation tables, antenna positioning mounts, and computer-controlled telescope mounts. Of these, the telescope mounts are particularly appealing in that they offer very high precision computer control, but are popular enough to exhibit commodity pricing.
It is cheap and easy to build your own pan/tilt mount using servos, but positioning is generaly quite inaccurate. For example, simple servos, such as those used in radio controlled devices, typically provide only 256 distinguished positions with standard control interfaces. Active Robots Lynx B Pan & Tilt Assembly is a good packaged example of what you'd get building a servo set-up yourself.
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