Optical motion tracking

Motion Tracking can differ from Motion Capture because in applications such as sports and missiles the object of interest is tracked optically instead of a person. The technology is basically the same, with some differences in that many of the Optical Motion Tracking applications occur outdoors, requiring differing lens and camera configurations.

Applications

Optical motion tracking is used to keep track on various objects, including airplanes, launch vehicles and satellites. It has the advantage of providing high resolution image of the target being tracked. The image obtained from NASA's long-range tracking system on space shuttle Challenger's fatal launch provided crucial evidence about the cause of the accident. Optical tracking systems are also used to identify known spacecrafts and space debris despite the fact that it has a disadvantage over radar in that the objects must be reflecting or emitting sufficient light.^[1]

Design

An optical tracking system typically consists of 3 subsystems. The optical imaging system, the mechanical tracking platform and the tracking computer.

The optical imaging system is responsible for converting the light from the target area into digital image that the tracking computer can process. Depending on the design of the optical tracking system, the optical imaging system can vary from as simple as a standard digital camera to as specialized as an astronomical telescope on the top of a mountain. The specification of the optical imaging system determines the upper-limit of the effective range of the tracking system.

The mechanical tracking platform holds the optical imaging system and is responsible for manipulating the optical imaging system in such a way that it always points to the target being tracked. The dynamics of the mechanical tracking platform combined with the optical imaging system determines the tracking system's ability to keep the lock on a target that changes speed rapidly.

The tracking computer is responsible for capturing the images from the optical imaging system, analyzing the image to extract target position and controlling the mechanical tracking platform to follow the target. There are several challenges. First the tracking computer has to be able to capture the image at a relatively high frame rate. This posts a requirement on the bandwidth of the image capturing hardware. The second challenge is that the image processing software has to be able to extract the target image from its background and calculate its position. Several textbook image processing algorithms are designed for this task but each has its own limitations. This problem can be simplified if the tracking system can expect certain characteristics that is common in all the targets it will track. The next problem down the line is to control the tracking platform to follow the target. This is a typical control system design problem rather than a challenge, which involves modeling the system dynamics and designing controllers to control it. This will however become a challenge if the tracking platform the system has to work with is not designed for real-time and highly dynamic applications, in which case the tracking software has to compensate for the mechanical and software imperfections of the tracking platform.

Software

Traditionally optical tracking systems often involves highly customized optical and electrical subsystems. The software that runs such systems are also customized for the corresponding hardware components. Because of the real-time nature of the application and the limited size of the market, commercializing optical tracking software posts a big challenge.

One example of such software is OpticTracker, which controls computerized telescopes to track moving objects at great distances, such as planes and satellites.

Weaknesses and speculation

The high cost of optical tracking systems has made this a limited area of research, although with inexpensive CMOS cameras this is becoming more viable and will likely be replacing radar and other lower resolution technologies in the near future.

Leveraging the millions of cameras being developed for Cell Phones, Web Cams, and other applications, CMOS cameras will likely win in short range applications due to costs, even though the visible wavelengths are less optimal.

Radar tracking

Radar tracking is fundamentally lower resolution because the pulse repetition rate and sweep rates are lower, as well as the wavelengths are longer. Newer and higher frequency radar systems have increased resolution, and for most applications are sufficient, but the cost is still an issue.

See also

• Gunshot Location System

References

1. ^ Veis, G. (1963). "Optical tracking of artificial satellites". Space Science Reviews 2: 250–296. Bibcode 1963SSRv....2..250V. doi:10.1007/BF00216781.  edit

External links

• Phonect - Optical Motion Detection for the iPhone - www.phonect.me