Handheld laser-based vehicle speed measurement device incorporating an automatic number plate recognition (anpr) function

Abstract

Disclosed herein is a handheld speed gun incorporating automatic number plate recognition (ANPR) functionality. As the image size of a vehicle license plate varies depending on its distance from the speed gun, in the present invention the distance to the target vehicle is known through the functionality of the laser sensor so the size of the pixels for the number plate can be estimated. Since the image of the number plate may be tilted in a handheld device, the present invention compensates for this by use of the instrument's tilt sensor or through other compensation by use of the image itself.

What is claimed is: 
     
         1 . A handheld laser-based speed gun comprising:
 a processor;   laser signal transmitting and receiving sections coupled to said processor configured to determine a speed of a target vehicle based on changes in distance between said speed gun and said target vehicle over time;   a camera module coupled to said processor configured to capture images of a number plate on said target vehicle, wherein said camera module comprises an autofocus mechanism; and   an automatic number plate recognition (ANPR) module coupled to said processor in operative association with said camera module.   
     
     
         2 . The speed gun of  claim 1  further comprising a folded optical system for redirecting an image pathway from said target vehicle to said camera module. 
     
     
         3 . The speed gun of  claim 1  wherein said distance between said speed gun and said target vehicle is utilized by said ANPR module and said processor to estimate the size of pixels in said captured images of alphanumeric characters of said target vehicle number plate. 
     
     
         4 . The speed gun of  claim 1  wherein said camera module is a rolling shutter device. 
     
     
         5 . The speed gun of  claim 4  wherein said camera module is operative to scan an image of said target vehicle number plate on a line-by-line basis. 
     
     
         6 . The speed gun of  claim 4  wherein said ANPR module and said processor are operative to perform rolling shutter compensation on captured images from said camera module. 
     
     
         7 . The speed gun of  claim 1  further comprising a database of vehicle number plates of interest to authorities for comparison to said captured images of said target vehicle number plate. 
     
     
         8 . The speed gun of  claim 7  wherein said database of vehicle number plates resides in a memory portion of said speed gun. 
     
     
         9 . The speed gun of  claim 7  wherein said database of vehicle number plates resides remotely from said speed gun and is bidirectionally coupled to said speed gun by a cellular network. 
     
     
         10 . The speed gun of  claim 8  wherein said database of vehicle number plates resides remotely from said speed gun and is bidirectionally coupled to said speed gun by at least one of a WiFi or NFC network. 
     
     
         11 . The speed gun of  claim 8  wherein a user of said speed gun is alerted to a match of said target vehicle number plate with a selected one of said database entries of interest to said authorities. 
     
     
         12 . The speed gun of  claim 11  wherein said user is alerted by at least one of haptic, aural or visual indicators. 
     
     
         13 . A method for identifying a vehicle number plate of interest with a handheld distance ranging device comprising an image sensor, the method comprising:
 capturing an image of said vehicle number plate;   compensating said captured image to account for a determined distance of said ranging device to said vehicle number plate to produce a compensated image; and   determining if said compensated image resides in a database of said vehicle number plates of interest.   
     
     
         14 . The method of  claim 13  wherein said database resides on said ranging device or at a remote location operationally coupled to said ranging device. 
     
     
         15 . The method of claim  17  further comprising:
 indicating to a user of said ranging device that a match of said vehicle number plate to one of said database entries has been determined. 
 
     
     
         16 . The method of  claim 15  wherein said step of indicating is carried out by at least one of haptic, aural or visual indicators of said ranging device.