A device for controlling a stepper motor that drives a plurality of shutter blades. The movement and position of the movement of the rotor of the stepper motor is monitored to determine when the next step of the stepper motor should be stepped so that the rotation of the rotor will be known to cause the shutter blades to form the correct aperture size. The device may also be used to drive an automatic focusing mechanism and/or zoom.

Frequency domain processing is used to determine rapidly whether false signals are present, and to improve the accuracy of speed measurements by rejecting speed measurements that could be inaccurate due to the presence of false signals. A Doppler signal responsive to speed of a moving vehicle is generated by a Doppler radar transceiver. A digital computer transforms the Doppler signal into a frequency domain signal such as an energy spectrum, and the speed of the moving vehicle is computed from the weighted arithmetic mean of the energy spectrum. The mean value, however, is rejected as an indication of speed if the variance of the energy spectrum from the mean exceeds a threshold, or if a differential of the spectrum with respect to frequency exceeds a threshold. The frequency domain processing of the present invention can also be used to reject certain bands of frequencies in the Doppler signal, such as bands of frequencies that differ from the mean value by more than a threshold, and the mean value can then be recomputed to provide an even better indication of the speed of the moving vehicle. Moreover, speed samples computed from successive frames of spectrum can be averaged, and the average value can be rejected as an indication of speed if the variance of the speed samples about the average value exceeds a threshold, or if the difference between successive speed samples exceeds a threshold.

A traffic monitoring system has a common housing for a Doppler radar transceiver, a video camera, and a digital computer for processing the Doppler signal. The system also includes a video cassette recorder, a high-speed photographic camera, and a laptop computer for downloading control settings and a program from a diskette or memory card to the digital computer. The digital computer performs an initial self-test by injecting a calibration signal in lieu of a Doppler signal into an electronic interface between the radar transceiver and the digital computer. The radar transceiver generates a Doppler signal having two channels, and the phase between the channels indicates whether a vehicle is approaching or receding from the radar transceiver. The two channels are recorded on the left and right audio channels of the video cassette. Recorded with the video signal is a push-down stack of speeds of vehicles detected on the system, in order to present a record of prevailing traffic conditions when prosecuting a speed violator. The recorded picture may also include a series of successive speed measurements for each vehicle. Although an operator could listen to the Doppler signal, it is preferred that the digital computer activates an audio annunciator to emit a click sound when the system detects a vehicle, and a warbly sound when a detected vehicle exceeds a specified speed limit.

An apparatus of the invention includes a device for triggering a camera to photograph a vehicle within a traffic intersection, where the triggering of the camera is dependent on the speed of the vehicle before entering the intersection and may also be dependent on presence information. The device includes a sensor system (or "sensor array") to transmit signals corresponding to a moving vehicle and a control system for processing the signals and triggering the camera. The signals preferably include "position signals" from which a transit time can be calculated, and "presence signals," from which presence information can be obtained, particularly the location of the rear of the vehicle or the location of the rear wheels of the vehicle. A trigger time for taking a picture of the vehicle may be calculated from the transit time. A method of the invention includes the step of transmitting signals to a control system in response to the vehicle passing over a first traffic sensor and corresponding to the speed of the vehicle. The method may also include the steps of transmitting presence signals to the control system, preferably corresponding to the presence of the vehicle in a known presence zone outside the intersection, and photographing the vehicle in response to those signals. The system preferably uses a first set of signals (reflecting vehicle speed or transit time) and a second set of signals (reflecting the presence of the vehicle) to determine when to trigger the photograph of the vehicle in the intersection zone.

A traffic violation processing method is disclosed, which includes the steps of monitoring a vehicle; determining whether the vehicle is in violation of a traffic violation and recording the image of the vehicle on a camera when the vehicle is determined to have violated a traffic violation; providing a digital image of the vehicle; recording and storing deployment data corresponding to the violation, wherein the deployment data includes an identifier associated with the traffic violation; assigning the identifier to the digital traffic image; storing the digital image of the vehicle, together with the identifier, on a storage medium; matching the deployment data with the stored digital image by correlating or matching the identifier associated with the deployment data with the identifier associated with the stored digital image; and generating a traffic document that includes the stored digital image and the deployment data.