Patent Description:
The present invention relates, in general, to the field of handheld laser-based vehicle speed measurement devices and speed guns. More particularly, the present invention relates to a handheld laser-based vehicle speed measurement device incorporating an automatic number plate recognition (ANPR) function.

Laser Technology, Inc. assignee of the present invention, has previously introduced the TruCAM® (a registered trademark of Laser Technology, Inc. ) video laser-based vehicle speed measurement device which incorporates the industry's first video camera in a handheld form factor. In operation, it collects and stores a complete chain of video evidence for both speeding and tailgating violations along with a high-resolution image that identifies the vehicle make, model and license plate number. Representative of the technology embodied in the TruCAM devices is that disclosed in, for example, in <CIT>; <CIT> and <CIT>, the disclosures of which are herein specifically incorporated by this reference in their entirety as if fully set forth herein.

Laser-based speed measurement devices, operate to calculate distance by measuring the time of flight of very short pulses of infrared light. That is, a measurement is made as to the time it takes one or more laser pulses to travel to a target vehicle and back with a precision time base. With knowledge of the constant speed of light, the distance the laser pulses have traveled can then be calculated. If the speed gun takes, for example, a thousand samples per second, its processor can compare the change in distance between successive samples and thereby calculate the speed of the target vehicle. By taking several hundred samples over the course of a fraction of a second or so, the accuracy can be extremely high.

Conventional, fixed position, automatic number plate recognition (ANPR) is a technology that uses optical character recognition on images to read vehicle registration plates to create vehicle identification data. At present, it can be implemented using closed-circuit television, fixed traffic enforcement cameras, or other cameras specifically designed for the task. ANPR is used by police forces around the world for law enforcement purposes, including to check if a vehicle is currently being sought for whatever reason, registered and/or licensed. It is also used for electronic toll collection on pay-per-use roads and as a method of cataloguing the movements of traffic, for example by highways agencies.

Automatic number plate recognition can be used to store the images captured by the cameras as well as the text from the license plate, with some configurable to store a photograph of the driver. Systems may also employ infrared lighting to allow the camera to take the picture at any time of day or night.

<CIT> describes a speed measurement system for measuring speeds of vehicles, capturing images of vehicles, and detecting violation of stop sign and traffic signal laws. The system includes a laser speed detector for determining a speed of a vehicle adjacent a stop sign. When a speed is determined, the detector generates a speed signal. The system includes a camera generally aligned with the speed detector operable to capture and store digital still images of vehicles in memory. The camera is programmed to respond to an image capture signal to generate and transmit a digital image file including a still image of the vehicle targeted by the detector. A portable processor is linked to the speed detector and the camera to first receive the speed signal, to compare the detected speed with a threshold speed, to transmit an image capture signal to the camera, and to receive the image file from the camera.

Heretofore, ANPR functionality has not been able to be implemented in a handheld speed measurement device, whether implemented in conjunction with radar or laser-based speed measurement devices. Particularly, all existing ANPR equipment utilize and assume predetermined geometries between the instrument and the vehicle license plate (inclusive of optical parameters and distances to plate) in order to properly function. Moreover, such existing products are not capable of accurately functioning when tilting of the device must be compensated for as in the operation of a handheld device such as a laser-based speed measurement device as disclosed herein.

The invention is defined by the subject matter of the independent claim <NUM>. embodiment of the present invention, both techniques may be employed.

Typical low-cost cameras, such as those incorporated in "Body CAMs" and smart phones, utilize what are known as rolling shutters. Such cameras take an image line-by-line instead of the whole scene at once. On the other hand, with a conventional "wet film" a "global shutter" is employed wherein the camera shutter is mechanically opened. In contrast, modern cameras utilize an electronic shutter so a line-by-line technique is employed.

In any event, when a vehicle (or the speed gun itself) is moving the image of the vehicle license plate is at least somewhat distorted. Consequently, the technique of the present invention incorporates rolling shutter compensation and pre-processing of the license plate image.

As with any handheld device, power considerations are also important as most will be battery powered. Consequently, the processing algorithms are advantageously "lighter" and less computationally intensive. The principles of the present invention are readily implemented in a self-contained device such as an "off-line Body Cam" and may be coupled to a database to provide appropriate notice to a user of the speed gun when a "wanted" vehicle license plate is found through connection to a cellular network, WiFi connection or the like.

Particularly disclosed herein is a handheld laser-based speed gun comprising a processor and laser signal transmitting and receiving sections coupled to the processor for determining a speed of a target vehicle based on changes in distance between the speed gun and the target vehicle over time. The speed gun further comprises a camera module coupled to the processor for capturing images of the target vehicle number plate and an automatic number plate recognition (ANPR) module is also coupled to the processor in operative association with said camera module.

Also particularly disclosed herein is a method for identifying a vehicle number plate of interest with a handheld distance ranging device comprising an image sensor. The method comprises capturing an image of the vehicle number plate; compensating the captured image to account for a determined distance of the ranging device to the vehicle number plate to produce a compensated image; and determining if the compensated image resides in a database of the vehicle number plates of interest.

The aforementioned and other features and objects of the present invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of a preferred embodiment taken in conjunction with the accompanying drawings, wherein:.

With reference now to <FIG>, an isometric view of a representative laser-based speed gun <NUM> is shown incorporating a camera module and folded optical system <NUM> incorporating an ANPR function in accordance with the principles of the present invention. The laser-based speed gun <NUM> comprises a housing <NUM> and associated handle <NUM> for handheld operation. A trigger <NUM> is provided to initiate the transmission and reception of laser pulses toward a moving object, such as a vehicle, as well as initiate the recording of video of the object in conjunction with the camera module and folded optical system <NUM>. The laser-based speed gun <NUM>, as illustrated, includes a display <NUM>, user input and selection elements <NUM> as well as target vehicle sighting optics <NUM>. A representative laser-based speed gun may be implemented in accordance with the disclosure of commonly owned <CIT>", the disclosure of which is specifically incorporated by this reference in its entirety as if fully set forth herein.

With reference now to <FIG>, a representative functional block diagram of the laser-based speed gun <NUM> of the preceding figure in accordance with the principles of the present invention is shown.

The exemplary speed gun <NUM> comprises a microprocessor <NUM> or central processing unit (CPU) with an associated oscillator <NUM> (where required) for providing clocking signals to the microprocessor <NUM>. A battery and power management section <NUM> supplies operating power to the microprocessor <NUM> and various other speed gun subsystems (not shown) as well as the high voltage (HV) power supply <NUM> which provides operating voltage to a laser transmit section <NUM> and associated laser diode as well as a laser receive section <NUM> and associated photodiode.

The laser receive section <NUM> receives a portion of the laser energy transmitted by the laser transmit section <NUM> as reflected by a target vehicle to a photodiode and provides the return signals to a signal/noise (S/N) discriminator section <NUM> in order to separate true return pulses from any associated noise. A timing section <NUM> accurately measures the time between the transmission of laser pulses from the laser transmit section <NUM> and the reception of the same target vehicle reflected pulses at the laser receive section <NUM> to determine, in conjunction with the microprocessor <NUM>, the varying distance, and hence the speed, of the particular target vehicle towards which the speed gun <NUM> is aimed.

A fire button <NUM> is coupled to the battery and power management section <NUM> and is operable by a user of the speed gun <NUM> in conjunction with the microprocessor <NUM> to determine when to emit pulses toward a target vehicle from the laser transmit section <NUM>.

The speed gun <NUM> may also incorporate a user viewable in-sight display <NUM> implemented in conjunction with a novel and proprietary backlighting technique which may include a view of the target vehicle in conjunction with an aiming reticle as well as information regarding the range to, and/or speed of, the target vehicle, battery condition and other information. In certain embodiments, the speed gun <NUM> may also comprise a touchscreen display to allow user to provide inputs to the speed gun <NUM> in conjunction with, or as an alternative to, an input/output (I/O) section <NUM>.

The I/O section <NUM> may further comprise a keypad or other means of communicating information to or from the microprocessor <NUM> including wired connections such as a universal serial bus (USB) and the like as well as wireless connections such as an IEEE <NUM> (WiFi), or other wireless local area network (WLAN) transceiver; a Bluetooth transceiver or other personal area network (PAN) system for wirelessly exchanging data over short distances; and/or another near field communication (NFC) transceiver (inclusive of infrared (IR) coupling) for wirelessly coupling the speed gun <NUM> to external devices or data storage elements.

As illustrated, the speed gun <NUM> may further include one or more of additional input modules such as an inclinometer <NUM>, accelerometer, <NUM>, magnetic sensor <NUM> (e.g. a compass) and/or rate gyro <NUM>.

As an exemplary utilization of a backlighting technique for LCDs and other display devices in electronic speed guns or the present invention, the speed gun <NUM> is illustrated as incorporating a backlight <NUM>. In a representative embodiment of the speed gun <NUM> of the present invention, the backlight <NUM> may be advantageously provided in accordance with the specification and teachings of commonly owned <CIT>", the disclosure of which is specifically incorporated by this reference in its entirety as if fully set forth herein.

As further illustrated, the speed gun <NUM> may comprise a reticle <NUM> interposed between the backlight and the in-sight display <NUM> as is more fully described in the aforementioned '<NUM> patent. A global positioning satellite (GPS) module <NUM> may also form a portion of the speed gun <NUM> to provide information to the microprocessor <NUM> as to the specific geographic position of the speed gun <NUM>. In addition, and as previously noted, the speed gun <NUM> may further include an NFC module <NUM> capable of enabling external bidirectional communication with the speed gun <NUM> via Bluetooth, WiFi and the like in conjunction with a smartphone, tablet device, computer laptop etc..

In an alternative embodiment of the present invention, the speed gun <NUM> may further be configured to provide an augmented reality display to a user by the additional provision of an advanced in-scope display or camera module <NUM> and view screen <NUM>. In this manner, by angularly scanning the speed gun <NUM> about a target vehicle, other features and objects in the surrounding scene can be displayed in the view screen <NUM> (or in-sight display <NUM> and/or the screen of an associated smartphone, tablet device or laptop) to a user of the speed gun <NUM> along with the determined distances to such additional features and objects to provide additional terrain context over and above the speed of, or distance to, the desired target vehicle. Such features and objects might be, depending on the particular application of the speed gun <NUM> trees, highway overpasses, signs, buildings and the like. The in-scope display or camera module <NUM> is then operational to log the surrounding features and objects, and their distances determined by the laser-based speed gun <NUM> and this information displayed in a picture to a user of the speed gun <NUM>, whether on the speed gun itself or on the screen of any associated device.

With reference additionally now to <FIG>, an additional representative portion of the functional block diagram of the laser-based speed gun <NUM> of the preceding figure is shown illustrative of an embodiment of the present invention which may further include a vibro-motor <NUM> and one or more audio and/or visual indicators <NUM> to provide physical, haptic and audible and/or visible feedback to the user of a particular target vehicle number plate being of interest. A laser-based speed gun <NUM> in accordance with the present invention will include an ANPR function block <NUM> as illustrated and may further include a cellular telephony block <NUM> and/or WiFi block <NUM>, and/or NFC or other communications medium, to bidirectionally communicate data regarding a vehicle's license plate number as well as speed and other information to/from a location and database remote from the laser-based speed gun <NUM>. The ANPR function block <NUM> is operative in conjunction with the microprocessor <NUM> and the camera module <NUM> as will be more fully disclosed hereinafter.

A system comprising the laser-based speed gun <NUM> may further include a database <NUM> either resident in the laser-based speed gun <NUM> itself or remotely therefrom in communication with said laser-based speed gun <NUM>. The database <NUM> may, for example, comprise number plates of particular interest to authorities which can then be matched to the number plate of a target vehicle as determined by the ANPR functionality. This information can be added to the database <NUM> or communicated to the operator of the laser-based speed gun <NUM> by haptic or aural and/or visual means by virtue of vibro-motor <NUM> and the aural visual indicator <NUM>.

With reference additionally now to <FIG>, a representative flow chart of one possible implementation of a laser-based speed gun <NUM> incorporating an ANPR function <NUM> in accordance with the principles of the present invention is shown. The representative ANPR process includes determining the distance to the target vehicle license plate as determined by the laser rangefinder and as computed by the processor <NUM> at step <NUM>. The speed gun <NUM> then computationally resizes the image of the license plate based on the computed distance at step <NUM>.

The height and location of the license plate is then obtained at step <NUM> and the segmented data is then copied into the work area of the processor <NUM> along with tilt compensation information derived from, for example, the inclinometer <NUM> (<FIG>) as shown in step <NUM>. At step <NUM>, the data is once again segmented and a new segment determined on the raw data at step <NUM>. A further segment operation is performed at step <NUM> and the data is split, if required, at step <NUM> along with a merge operation at step <NUM> if also required.

At this point a neural network is applied to each segmented zone in order to obtain the particular alpha or numerical character being considered at step <NUM>. If another character of the license plate needs to be determined at decision step <NUM>, then the ANPR process returns to step <NUM> to continue the ANPR function <NUM>.

With reference now to <FIG>, various views of an example license plate are shown illustrative of a representative ANPR function implemented in conjunction with a speed gun in accordance with the principles of the present invention.

With reference specifically to <FIG>, a representative image of a license plate is shown. In general, the technique of the present invention performs well if the width of each character in the image is approximately <NUM> pixels or greater. In <FIG>, an average 3x3 filter is applied to the image. In the TruCam2® instrument available from Laser Technology, Inc. , assignee of the present invention, this filter operation is performed by a Neon processor employing single instruction multiple data (SIMD), which employs and architecture for the ARM Cortex-A series and Cortex-R52 processors.

With respect to <FIG>, edge detection of the image is performed in the X direction only and in <FIG>, adjacent segments or the characters are grouped. <FIG> shows the license plate character candidates being grouped and tilt compensation being applied.

The representative license plate image is shown in <FIG> with anti-aliasing having been applied and, as shown in <FIG>, following a rolling shutter compensation operation. Anti-aliasing is then again applied as shown in <FIG> and the characters of the license plate segmented (after rolling shutter compensation) in <FIG>.

Although not specifically illustrated, the ANPR function of the preceding figures may also advantageously incorporate steps such as the trimming of the license plate characters, the application of a neural network, the retrieval of data and the application of the process with respect to license plates having two rows of alpha and numeric characters. The technique of the present invention is also applicable to those number plates having, for example, Cyrillic, Chinese, Korean, Japanese characters or Arabic alphabet representations.

While there have been described above the principles of the present invention in conjunction with specific apparatus, it is to be clearly understood that the foregoing description is made only by way of example and not as a limitation to the scope of the invention. Particularly, it is recognized that the teachings of the foregoing disclosure will suggest other modifications to those persons skilled in the relevant art. Such modifications may involve other features which are already known per se and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure herein also includes any novel feature or any novel combination of features disclosed either explicitly or implicitly or any generalization or modification thereof which would be apparent to persons skilled in the relevant art, whether or not such relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as confronted by the present invention. The applicants hereby reserve the right to formulate new claims to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claim 1:
A handheld laser-based speed gun (<NUM>) comprising:
a processor (<NUM>);
laser signal transmitting and receiving sections (<NUM>, <NUM>) coupled to said processor for determining a speed of a target vehicle based on changes in distance between said speed gun and said target vehicle over time;
a camera module (<NUM>) coupled to said processor for capturing images of said target vehicle number plate, wherein the captured images of the target vehicle number plate comprise alphanumeric characters; and
an automatic number plate recognition (ANPR) module (<NUM>) coupled to said processor in operative association with said camera module, wherein the distance between said speed gun and said target vehicle is utilized to resize the images of the license plate for input into the ANPR module.