Patent GB-1304973-A (GB)
IPC: G08G1/01
Filed: 1971-04-19
Abstract: 1304973 Road traffic measurements; digital measurement of dimensions SPERRY RAND CORP 19 April 1971 [16 April 1970] 25354/71 Headings G4H and G4Q [Also in Division H4] A Data Sensor comprises a pattern of contrasting portions arranged to be scanned by a scanning means, the pattern being arranged or disposed for at least partial effective obscuration by objects whose associated data is to be determined and the scanning means being operative to provide pulses corresponding to those scanned portions of the pattern which are not effectively obscured by the objects, the pulses being processed to determine the data. As shown, in a first embodiment of a traffic monitoring system, a pattern 10, on the roadway has contrasting portions 12, 12<SP>1</SP>. A T.V. camera 13 is mounted above the roadway. Camera 13 may be adjustably mounted for altering, by remote control, the field of view by pan, tilt, zoom or focus signals. In operation, vehicles obscure portions of pattern 10 to produce a composite video signal from camera 13, which is processed to determine data of the traffic, In a processing circuit (Fig. 2b), shaped video pulses are produced by a bi-stable device 27 to which the composite video signal is fed via filters 26, in response to pulse information in the video signal. The shaped video pulses are fed to a counter control logic circuit 28 which provides a signal to a counter 30 which counts the video pulses; counter 30 is a backward counting device which outputs to a zero detector 36 which provides an output when counter 30 attains a count of zero. The output from detector 36 is applied to a vehicle detect storage counter 38 whose output is supplied to a central control digital computer 40. The latter analyses signals from circuit 38 to provide traffic controlling signals. A T.V. monitor 48 displays the image of the composite video signals generated by camera 13. The processing circuit of Fig. 2b receives various control signals from a control circuit 58 (Fig. 2a). The latter includes line designation switches 64 (or digital electronic registers) which provide a preset number representative of a predetermined scanning line of the raster. Similarly, lane start designation switches 67 and lane width designation switches 68 provide numbers representative of the beginning and end of a predetermined portion of the predetermined scanning line, respectively. Camera 13 is mounted so that the scanning lines of the raster are parallel to pattern 10; thus, particular portions of particular scanning lines will scan pattern 10 and one of the particular scanning lines that intersects pattern 10 may be selected for deriving the data associated with the traffic. The video signal corresponding to the portion of the scanning line selected will comprise a series of pulses in accordance with the scanned contrasting portions 12, 12<SP>1</SP>. When a vehicle obscures a number of portions 12, 12<SP>1</SP> the number of pulses occurring during the frames when the pattern is obscured will be correspondingly diminished. The control circuit 58 functions to select the scanning line as well as that portion thereof that scans pattern 10. In addition, the control circuit 58 provides a Phase G signal which comprises a control pulse occurring coincidentally with the scanning of pattern 10 by the predetermined portion of the predetermined line of the scanning raster. During occurrence of the Phase G signal, the camera 13 provides the aforesaid sequence of video pulses. When the pattern 10 is unobstructed, the number of video pulses corresponds to the number of contrasting portions 12, 12<SP>1</SP>; however, when a vehicle obscures portions of the pattern 10, a non-zero count will be registered by counter 30 at the termination of the Phase G signal, the non-zero count being representative of vehicle width. A signal representative of vehicle presence is fed to the vehicle detect output storage 38 during those frames in which pattern 10 is obscured. The vehicle detect output storage 38 thus provides a continuous "presence" signal which a vehicle is obscuring pattern 10, on a continuous "absence" signal when pattern 10 is unobscured. The width of the pulse provided by the "presence" signal is a function of vehicle length and velocity. Vehicle velocity may be determined by use of a second, identical pattern 10 placed parallel to the first, but spaced therefrom down the length of the roadway. The time displacement between the two pulses from vehicle detect output storage 38 will be a function of vehicle velocity. Lane occupancy and queue length may be computed by the computer 40. The T.V. monitor 48 and various test facilities are used to adjust the switches 64 so that the predetermined portion of the predetermined scanning line coincides with the longitudinal centre line of pattern 10; similarly, switches 67 and 68 are adjusted so that the predetermined portion of the predetermined scanning line occurs precisely in coincidence with pattern 10. The camera 13 may also survey a second traffic lane 11<SP>1</SP>. In a second embodiment (Figs. 3 and 4, not shown), a pattern (80) is disposed longitudinally along the lane centre line. A T.V. camera (82) is mounted to view the roadway such that the lines of the scanning raster are parallel with the pattern (80). A buffer register (103) stores a binary word which has a number of bits equal to the number of contrasting portions of the pattern (80) scanned by the predetermined portion of the predetermined scanning line. The bit pattern of the binary word, of which one such is shifted into the register (103) for each video frame, is representative of the instantaneous traffic situation within the field of view of the camera. A sequence of binary words is thus transmitted to the computer (105); the sequence is representative of incremental changes in the traffic configuration. The computer will thus provide such data as vehicle presence and count, velocity, length, lane occupancy, vehicle spicing, and queue length.  A second pattern (80) may be provided in an adjacent lane. In this instance lane intercrossings may be determined. Alternatively or in addition, a pattern (92) may be arranged vertically with respect to the roadway by disposing it on an upright. A T.V. camera (94) is then mounted on an upright on the opposite side of the roadway. This arrangement allows a determination of vehicle heights. In a further embodiment (not shown) for use in darkness, a pattern located at the roadside is obscured by shadows cast by vehicles passing a light source. Alternatively, a light source may illuminate the road-mounted patterns, being energized automatically when ambient light falls below a certain level. Alternatively, the patterns may be constructed of light emissive material illuminated from beneath the roadway surface. The patterns may have black and white, or coloured contrasting portions. The system is also applicable to determining data associated with objects on a conveyer belt.