FIELD 
     The invention relates generally to vehicle direction indication devices generally and, more particularly, to a vehicle direction indicator device that utilizes information provided by a turn-by-turn navigation system for enhancing driving safety. 
     BACKGROUND 
     Modern cars have devices enabling drivers to express their intentions to other drivers with respect to upcoming stops or turns. The most common mechanism for indicating driving intentions is a signal lamp or light activated from within the vehicle and visible from outside the vehicle, e.g., turn/stop signal lamps. Such signaling lights are often found on the front and rear of vehicles. 
     Referring more specifically to turn signal lamps or other direction indicators, such indicators traditionally show only the direction (left or right) that the driver intends to turn the vehicle, and not the degree or timing of the turn. In complex road topology, however, left/right direction indicators are not enough. Drivers often misunderstand others&#39; direction intention so that the misunderstanding results in accidents. Even in a simple road topology, such a misinterpretation may happen due to the lack of information. 
     By way of example, a segment of US HWY 101 North includes, in very close proximity, the flowing possible right turns: right onto US 101, right to exit to Interstate highway 280, right to exit to Interstate highway 680, right to exit to Story Rd North, and right to exit to Story Rd South. If a tailing driver drives on US HWY 101 North at this point and sees that a car ahead is flashing its right turn signal, the right turn signal can be interpreted in many different ways, and is thus of little or no use to the driver of the tailing vehicle. 
     While the disclosed principles herein are directed at least in part to overcoming one or more disadvantages, noted or otherwise, it will be appreciated that the innovation herein is defined by the attached claims without to regard to whether and to what extent the specifically claimed embodiment overcomes one or more of the noted problems in the existing technology. 
     SUMMARY 
     A system for providing an externally visible signal regarding a navigational instruction at a vehicle includes a navigation system, a navigation message sender, a navigation message receiver, and a display system. The navigation system generates and outputs turn-by-turn navigational directions within the vehicle to assist a driver of the vehicle in reaching a given destination location. The navigation message sender receives the turn-by-turn navigational directions and transmits them to the navigation message receiver. The navigation message receiver provides a navigational message to the display system for display in a manner visible outside the vehicle. 
     In a further aspect, a method is disclosed for providing an externally visible signal at a vehicle to signal a trailing driver of an imminent turn of the vehicle. The method includes a number of steps including generating turn-by-turn navigational directions within the vehicle to direct a driver of the vehicle in reaching a given destination location, determining whether the driver of the vehicle has actuated a user-selectable turn indicator, and providing a message based on the turn-by-turn navigational directions to an external display system if the driver of the vehicle has actuated the user-selectable turn indicator, wherein a display surface of the external display system is visible outside the vehicle. 
     In yet a further aspect an apparatus is disclosed for alerting a vehicle non-occupant of an imminent turn of the vehicle. The apparatus includes a navigation interface and an external display device. The external display device is configured to be mounted to an external surface of the vehicle, and the navigation interface is configured to interface to an in-vehicle guidance system, a user-actuated turn signal, and the external display device, such that when the user-actuated turn signal is active, turn-by-turn directions are retrieved from the in-vehicle guidance system and a directional message based on the turn-by-turn directions is provided to the external display device for display to the non-occupant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the disclosed invention will be apparent from the following description taken in conjunction with the Figures, of which: 
         FIG. 1  is a schematic illustration of a system architecture according to an embodiment of the invention; 
         FIG. 2  depicts an example of display unit installation in a vehicle according to an embodiment of the invention; 
         FIG. 3  depicts an example of an alternative display unit installation in a vehicle according to an embodiment of the invention; 
         FIG. 4  depicts an example of yet another display unit installation in a vehicle according to an embodiment of the invention; 
         FIG. 5  depicts examples of navigational messages shown on the display system in an embodiment of the invention; and 
         FIG. 6  is a flow chart of a process according to an embodiment of the invention for coordinating a navigational message display with receipt of a turn signal. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment, the invention relates to a vehicle direction indicator device that utilizes information provided by turn-by-turn navigation systems to enhance driver safety. A device according to an embodiment may be connected wirelessly or otherwise and communicates with a turn-by-turn navigation system that provides detailed directions to a given destination via text, graphics, and/or speech. The navigation system, which is located within the vehicle, may be by way of pre-installed (before-market) head-unit-type navigation systems, portable navigation systems, and navigation software installed on multi-purpose mobile devices. 
     The device receives turn-by-turn navigation directions provided by the navigation system via wired or wireless networks and displays them on the display system. The display screen can be installed in any suitable location in or on the vehicle as allowed by law, such that drivers in following vehicles can observe navigation messages displayed on the display system. Navigational messages may have richer content than the binary (on/off) turn signal lamps of modern vehicles. The contents of the navigational messages may include but are not limited to a next action, an immediate destination, and a distance to a location where the next action should be taken. By knowing not just left or right, but also richer navigation information of a preceding driver, trailing drivers can predict a next driving action so as to avoid collisions or accidents due to misinterpretation of the preceding driver&#39;s intention. 
     An overall architecture of a system  100  according to an embodiment of the invention is shown in  FIG. 1 . The system  100  consists of Navigation System ( 101 ), Navigation Message Sender ( 102 ), Navigation Message Receiver ( 103 ), Display System ( 104 ), and User Signalling Interface ( 105 ). The Navigation System ( 101 ) provides turn-by-turn navigational directions to reach a given destination location using resources including by way of example only, but not limited to, maps, road topology database, real-time traffic information, historical routes database, etc. If no destination location is input by the driver, then the Navigation System ( 101 ) may or may not provide locational information. 
     The Navigation Message Sender ( 102 ) receives turn-by-turn navigational directions from Navigation System ( 101 ) and sends the direction messages to Navigation Message Receiver ( 103 ) via one or more wired or wireless networks. Turn-by-turn navigation directions may contain a specified action (e.g. turn right/left, go on, exit right/left, u-turn, etc.), an immediate destination (e.g. Fifth Ave, US HWY 101, Exit 89B), and/or a distance to a location where the action should be taken (e.g. 100 m, 4 miles). The Navigation Message Receiver ( 103 ) receives the navigational messages from Navigation Message Sender ( 102 ) and provides them to the Display System ( 104 ). 
     The Display System ( 104 ) receives the navigational messages from Navigation Message Receiver ( 103 ) and displays the messages in a textual and/or visual representation. The message transformation is used, for example, if the original navigational message is too long to fit into the display screen. For example, if the original message is “Escuela Avenue” can be transformed into “Escuela Ave.” In addition, if the transformed message is still too long to fit into the display screen, then animational display techniques may be utilized for effective display. For example, a text rotation technique wherein the displayed message is continuously shifted one letter by one letter towards left or right over time may be used. 
     In an embodiment, the Navigation Message Receiver ( 103 ) is connected to and acts in concert with a user signaling interface  105 . The user signaling interface  105  may be for example a user-actuated lever, button, or other element for causing a turn signal to be displayed by the vehicle. For example, the user signaling interface  105  may be a turn signal lever on the steering column. In this embodiment, when the Navigation Message Receiver ( 103 ) receives an “on” signal from the user signaling interface  105 , the Navigation Message Receiver ( 103 ), the Navigation Message Receiver ( 103 ) provides any navigational messages from the Navigation Message Sender ( 102 ) to the Display System ( 104 ). Similarly, when the Navigation Message Receiver ( 103 ) does not receive an “on” signal from the user signaling interface  105 , the Navigation Message Receiver ( 103 ) does not provide any navigational messages from the Navigation Message Sender ( 102 ) to the Display System ( 104 ). 
     Thus, in this embodiment, when a user signals a turn, the system signals which turn will be taken, but when the user is not signaling a turn, no navigational message is displayed. This optional feature helps to avoid display of a false navigational message signal that might otherwise occur if the navigation system provides a navigation instruction that the user chooses to ignore. 
     The system  100  may be implemented in hardware or software depending upon the usage environment. In a hardware embodiment, the components of the system other than the display system  104  are implemented as one or more dedicated integrated circuits (ICs) or circuit assemblies. In the case of separate ICs, the components may communicate wirelessly or via hard-wired interconnections. Generally, if those components of the system are implemented as a single assembly, or at least one component of the system, if those components of the system are implemented via separate ICs, will embody a processor to execute the functions of the system. 
     In a software embodiment, the components of the system  100  other than the display  104  are implemented as software components or modules, residing on one or more processor-equipped devices or units, e.g., the in-vehicle telematics unit or otherwise. It will be appreciated that in an embodiment wherein the described functions are software driven, such functions are executed via the computerized execution, by the processor, of computer-executable instructions stored on a tangible non-transitory computer-readable medium such as an optical, magnetic, or flash drive, or a PROM, EPROM, etc. 
     Wireless interconnections may be used in various embodiments, e.g., to the display system  104 , or between other components of the system  100 . In these embodiments, such wireless interconnections may be transient or permanent, and may be via any suitable protocol, e.g., BLUETOOTH, ZIGBEE (or other 802.15x), 802.11x, etc. 
     The Display System ( 104 ) can be installed in any part of vehicle where it may be legally placed and where drivers in trailing vehicles can see displayed navigation messages.  FIG. 2 ,  FIG. 3 , and  FIG. 4  depict non-limiting examples of different display unit installation in rear view of the vehicle. In particular, in  FIG. 2 , the display unit  201  is located on the lower part of the rear window  202  of the vehicle  200 . The display unit  201  may be located inside or outside the vehicle  200  depending upon whether the display unit  201  has been water-proofed, and the means of communication used by the display unit  201 . Thus, if the display unit  201  is waterproof and communicates with the rest of the system via a wireless channel, then it may easily be mounted externally. 
       FIG. 3  shows an alternative mounting the display unit  301 . In this embodiment, the display unit  301  is mounted on the roof  302  of the vehicle  300 . Similar to the latter embodiment discussed with respect to  FIG. 2 , the display unit  301  is preferably water-proofed and wirelessly linked in this embodiment. 
     As one final example, not intended to exclude other embodiments not explicitly shown,  FIG. 4  shows an alternative external mounting of the display unit  401 . In this embodiment, the display unit  401  is mounted on the rear bumper  402  of the vehicle  400 . Again, it is preferred but not required that the display unit  401  be water-proofed and be connected to the remainder of the system wirelessly. The latter preference would avoid needing to run hard wiring of the system upon installation and would allow easy repositioning of the system by the user. 
     Although the exact format and type of navigational message used in embodiments of the invention are not critical,  FIG. 5  illustrates several exemplary messages and their meaning. As can be seen, the message  501  “39B′ accompanied by a right arrow may mean “exit right on 39B.” Similarly, the message  502  “Fifth Ave” may correspond to the direction “turn left on 5 th  Avenue.” As can be seen, while certain messages may have both a direction and a textual message, other messages only have a textual content, as with messages  503  and  504 . Thus, message  503 , i.e., “US HWY 101” corresponds to a direction of “Proceed on US HWY 101” while the message  504  “U Turn” corresponds to a direction of “U-Turn Ahead.” 
     A process  600  for displaying navigational messages is shown in the flow chart of  FIG. 6 . The process  600  begins at stage  601 , wherein the Navigation Message Receiver  103  determines whether a turn signal has been received from the user signal interface  105 . If a turn signal has been received from the user signal interface  105 , the process  600  flows to stage  602 , wherein the Navigation Message Receiver  103  determines whether the received turn signal is consistent with a current instruction of the system. For example, if a left turn signal is received, and the current navigational instruction is to take a left turn on HWY X, then the turn signal and navigational instruction may be deemed consistent. On the other hand, if a left turn signal is received and the current navigational instruction is to bear right on Exit 1, then the turn signal and navigational instruction may be deemed inconsistent. 
     If at stage  602  it is determined that the received turn signal is consistent with a current instruction of the system, then the Navigation Message Receiver  103  sends the current instruction or an abbreviation thereof to the display system  104  at stage  603 . Otherwise, the process  600  returns to stage  601 , where the Navigation Message Receiver  103  awaits receipt of a turn signal. 
     It will be appreciated that a new system and method of conveying navigational instructions in conjunction with a turn signal has been disclosed. All references herein, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
A system for providing an externally visible signal regarding a navigational instruction at a vehicle includes a navigation system, a navigation message sender, a navigation message receiver, and a display system. The navigation system generates and outputs turn-by-turn navigational directions within the vehicle to assist a driver of the vehicle in reaching a given destination location. The navigation message sender receives the turn-by-turn navigational directions and transmits them to the navigation message receiver. The navigation message receiver provides a navigational message to the display system for display in a manner visible outside the vehicle.