FIELD OF THE INVENTION 
     Embodiments of the present invention are related to systems and methods for personnel rescue, and particularly to locating personnel via traversal path retracing. 
     BACKGROUND OF THE INVENTION 
     Firefighters and other rescue workers often put themselves in harm&#39;s way. A firefighter may enter a burning building, filled with smoke and falling debris, and make his way through various rooms, hallways, stairwells, etc., in an effort to find a source of smoke or fire, to locate possible victims, and/or to secure a given area. Unfortunately, as a result of the dangerous environment, including fumes, heat, sharp objects, it is not too uncommon for a firefighter to be injured and or incapacitated in the course of his work. When this occurs, it is imperative that the firefighter be quickly located and evacuated from the area for treatment. However, in the event the firefighter (or other personnel) is, e.g., working alone, and an incapacitating injury occurs, or the firefighter simple wants assistance with whatever the task at hand might be, it is necessary for others to know where the firefighter can be found so that a rescue team or other assistance can be dispatched to that location. It is critical for a rescue team to know at least the specific floor and better if possible the specific room where a downed firefighter can be found so that rescue can be done quickly before he or she runs out of oxygen. 
     U.S. Pat. No. 6,898,559 to Saitta discloses a system for dynamic and automatic building mapping in which a tracker module is carried by a user and an optional command module which, together, operate to automatically map the rooms of a building as a user traverses the rooms of the building. The tracker module includes a transducer system that determines the present distance from the user to each of the walls of the room, the location of openings in the walls as well as an inertial guidance system that precisely locates the user with respect to a known reference point. The data produced by the tracker module of the automatic building mapping system can be transmitted to a centrally located command module so that multiple units can simultaneously be tracked and a mapping of the building effected from different perspectives to thereby create an accurate composite layout map. In addition, the user can receive a heads-up display to enable the user to visualize the layout of the building as the user traverses the various rooms of the building, and as concurrently mapped by other users in the building. In this way, an accurate virtual map of a given building can be created on demand by users moving through the rooms of the building. While the system disclosed in the foregoing patent may have certain advantages, it is relatively complicated to implement. Moreover, for purposes of locating an individual in a rapid and efficient manner, the system disclosed by Siatta may not be the most appropriate. 
     In another related technology, U.S. Patent Publication No. 2009/0051768 A1 to DeKeyser discloses loop recording with book marking where recorded data can be transmitted wirelessly to another location. However, such a system is not necessarily suitable for rescue operations of the type noted above. 
     Accordingly, other systems and methods for locating personnel are desired. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide a rescue apparatus that includes a user device configured to collect and transmit video data and inertial motion unit (IMU) data associated with the video data, and a rescue device configured to receive the video data and IMU data associated with the video data transmitted by the user device, to play the video data on a display, and further configured to present viewable indicia, based on the IMU data associated with the video data, that is indicative of the motion of a user when the video data was collected by the user device. 
     More specifically, in accordance with one embodiment of the invention, a firefighter (or other person/user) carries a user or “firefighter” device that includes a camera and an IMU. The camera is preferably mounted on the user&#39;s helmet in a forward looking direction to capture what the firefighter is seeing. As video data is being collected by the camera, the IMU generates direction, speed, tilt, and/or acceleration data that is indicative of the orientation and/or movement of the firefighter. In one embodiment, the IMU also incorporates ultrasonic sensors that can be used to detect, among other things, when the firefighter passes through a small passage, such as a doorway. 
     The video data and IMU data associated with the video data are streamed/transmitted to the rescue device (or first to a base station) that may be a handheld computer or wrist-mounted device. During a rescue mission, the video data is replayed on the rescue device along with indicia based on the IMU data associated with the video data, as well as, possibly, real-time IMU data generated with respect to the rescuer who is operating the rescue device. 
     Thus, for example, the rescue device might superimpose a direction arrow on the video imagery by using IMU data recorded at that time, or indicate that a doorway was passed through, or how much time has elapsed for the video along with the actual time the rescuer has been moving. 
     Ultimately, by watching the video and being further prompted by one or more indicia superimposed on the video being displayed, a rescuer may be able to more easily retrace the path of the firefighter and thus locate him. 
     These and other features of the several embodiments of the invention along with their attendant advantages will be more fully appreciated upon a reading of the following detailed description in conjunction with the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a plan view of a building along with a traversal path. 
         FIG. 2  depicts a firefighter device in accordance with an embodiment of the present invention. 
         FIG. 3  depicts a firefighter carrying the firefighter device in accordance with an embodiment of the invention. 
         FIG. 4  shows a configuration including several rescue devices in communication with a base station in accordance with an embodiment of the present invention. 
         FIG. 5  depicts a rescue device in accordance with an embodiment of the present invention. 
         FIG. 6  shows a rescuer carrying the rescue device in accordance with the present invention. 
         FIG. 7  shows an example display of the rescue device in accordance with an embodiment of the present invention. 
         FIG. 8  illustrates an example process that is performed in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIG. 1 , there is shown a plan view of a building  10  along with a traversal path  101  that a firefighter might take. As shown, traversal path  101  begins outside of building  10 , passes through an entryway  104 , follows a stairwell  106  (e.g., up one floor), passes down a hallway  108 , through a first door  110  and then a second door  112 , arriving in room  114 . It is at this location that a firefighter (or other person) may be in need of assistance, but for unknown reasons, is unable to describe to others where his location actually is. For example, it may be the case that the firefighter is disoriented, and simply cannot remember the route that he took to arrive in room  114 . Perhaps, also, the route that was taken was full of smoke and, as a result, the firefighter cannot describe the route because it could not be seen very well. It may also be the case the firefighter has become incapacitated and is, therefore, unable to provide any information to a rescue party. 
     Rescue parties often rely on global positioning system (GPS) coordinates to locate missing people or people in need of assistance. While this technology works very well outdoors, GPS signals often do not penetrate buildings, and thus may be ineffective for helping to locate someone indoors. 
     Thus, a goal of embodiments of the present invention is to facilitate locating a person, such as a firefighter, without already knowing their precise location. 
     Embodiments of the present invention comprise two main components: a firefighter device and a rescue device. Those skilled in the art will appreciate that these two main components may each be comprised of two or more sub-components, and that the number of sub-components is a matter of design. 
       FIG. 2  depicts a firefighter device  200  in accordance with an embodiment of the present invention. Firefighter device  200  includes a power supply  202 , a camera  204 , an inertial motion unit (IMU)  206 , memory  210 , microprocessor  212  and radio frequency (RF) link  214 , all connected via communication and/or power bus  220 , as shown. Power supply  202  can be any battery, preferably rechargeable. Power supply  202  could also be made available via another device carried by the firefighter  300  ( FIG. 3 ), such as a radio or other computing device. 
     Camera  204  is preferably a digital camera that can be controlled to capture images at a predetermined frame rate and is preferably attached to a helmet  302  of firefighter  300  and is preferably oriented forward. Camera  204  may be physically wired to other components of the firefighter device  200 , or may operate in a wireless fashion. 
     IMU (Inertial Motion Unit)  206 , in accordance with an embodiment of the present invention, can be considered an “umbrella” term that may represent one or several different devices whose data can be collected separately, and/or whose data can be collected and then combined to provide pre-calculated information. More specifically, IMU  206  may comprise any one or more of a gyroscope, accelerometer, compass, tilt sensor (not shown), ultrasonic sensors  310 , as well as other sensors or detectors and that may be appropriate for a given situation. These sensors and devices are well-known to those skilled in the art. Such sensors capture the motion acceleration (in both orientation and position). By integrating provided readings, the speed/velocity of the firefighter&#39;s motion can be obtained. The speed, orientation and position is recorded to indicate on the rescue device the direction of motion which can be indicated as an arrow (is the user going forward, backward, left, right, turning left or right, etc.). As shown in  FIG. 3 , the firefighter  300  may wear the firefighter device  200  using, e.g., a shoulder strap  301 , or the firefighter device  200  could be placed in a pocket or in a backpack worn by the firefighter  300 . In a preferred implementation, the firefighter device  200  is attached to an existing vest, belt, or oxygen bottle so as to avoid adding an entirely new device that could get in the way of a firefighter. 
     A gyroscope (one, two or three axis), if part of IMU  206 , could thus report the orientation of the firefighter with respect to some starting position. An accelerometer (single or multi-axis) can provide information about the changes in direction that the firefighter  300  may take as he follows the path  101  ( FIG. 1 ). A compass may likewise provide direction information with respect to the current direction of motion. Finally, and optionally, one or more ultrasonic sensors  310  could be arranged, e.g., on helmet  302 . Such ultrasonic sensors can be used to detect when firefighter  300  passes through a smaller opening such as a doorway. 
     Microprocessor  212  preferably receives the sensor information from IMU  206  and at least buffers the same in memory  210 . In an alternative embodiment, as mentioned, microprocessor  212  may process data received from IMU  206  to generate blended or consolidated information, such as vector (speed and direction) information. 
     It is noted that memory  210  (e.g., a first-in, first-out (FIFO) device) need only be of sufficient size to store video data and IMU data for a time sufficient to transmit the data to base station  400  (or directly to a rescue (or locating) device  500 ) or of sufficient size to store data to be transmitted later in case the firefighter is not in range of the base station or the rescue device (note that the firefighter device might not be in range of the base station  400  (see  FIG. 4 ) during the rescue  500 , but the rescue device could come into range of the firefighter device  200  as the rescue team advance in the building, and as it comes in range, the rescue device  500  could get data that the base station  400  could not). Of course, memory  210  of firefighter device  200  could also be large enough to store the entirety of the data that is collected during the entirety of a sortie by the firefighter  300 . 
     To save memory usage, in one embodiment, the frame speed of the camera  204  may be linked or tied to the speed of the firefighter  300 . The speed of firefighter  300  may be obtained from IMU  206 . In any event, generally, a low, fixed frame speed of about one to ten frames/second may be sufficient to provide sufficient video imagery. 
     Ultimately, selected or all of the IMU data and the video imagery (data) captured by the camera is wirelessly transmitted from firefighter device  200  (via RF link  214 ) to a base station  400  ( FIG. 4 ) or directly to one or more rescue devices  500  ( FIG. 5 ). 
     Briefly,  FIG. 4  shows an embodiment wherein several rescue devices  500  are physically attached or in communication with a base station  400 . In this embodiment, firefighter device  200  communicates with base station  400  and transmits the video data and IMU data that has been collected and buffered in memory  210 . Although not shown, base station  400  would also comprise sufficient memory to store the data received from firefighter device  200 , or at least sufficient memory to pass the received data to memory  510  of rescue device  500 . The base station  400  facilitates loading several rescue devices  500  at the same time. However, those skilled in the art will appreciate that base station  400  is not essential, and data from firefighter device  200  could be passed directly to rescue device(s)  500 . 
     Reference is now made to  FIG. 5 , which depicts a rescue device in accordance with an embodiment of the present invention. Rescue device is preferably in the form of a tablet computer or wrist-mounted device and comprises a power supply  502 , such as a rechargeable battery, and an IMU  506  that includes at least some of the same devices or sensors as IMU  206  of firefighter device  200 . Rescue device  500  still further preferably comprises memory  510  and microprocessor  512 . The functionality of microprocessor  512  will be explained further below with reference to  FIGS. 7 and 8 . Rescue device  500  further includes one, or both, of an RF link  514  or a physical connection device such as a universal serial bus (USB) connector  515 . If USB connector  515  is used, then any rechargeable battery associated with power supply  502  could be recharged via the USB connector  515 . 
     In addition to the foregoing, rescue device  500  preferably comprises video processor  520  and display  522 . Video processor  520  could also be incorporated with microprocessor  512 . A general purpose of the rescue device  500  is to obtain the previously recorded video data and IMU data from firefighter device  200  and replay the video imagery on display  522  while trying to retrace the path of the firefighter  300  through building  10 . That is, in the case where firefighter  300  traverses a path while capturing video imagery/data and IMU data associated with that video data, and that firefighter  300  becomes incapacitated and/or requires assistance but cannot identify to a rescuer his location, the rescue device  500  can be used by rescuer  600  ( FIG. 6 ) to help retrace the path taken by firefighter  300 . As will be explained below, even when the video imagery presented on the display might be missing or difficult to see by the rescuer  600 , additional indicia based on the IMU data associated with the video data, as well as real-time IMU data collected with respect to the rescuer  600 , can provide sufficient information to the rescuer  600  to enable him to continue along the proper path to reach firefighter  300 . 
     More specifically,  FIG. 7  illustrates an example display  522  and additional features of rescue device  500 . As shown, display  522  depicts an image of what firefighter  300  might have seen prior to passing through doorway  110  ( FIG. 1 ), with a door on the left, which the firefighter may have looked at momentarily. Overlaid on the image is an arrow  702  (one possible indicia in accordance with an embodiment of the present invention) that indicates that the next direction the firefighter  300  took along his path is to the right, namely through doorway  110 . In other words, not only does the rescue device provide playback of the video data taken by firefighter  300 , but it enhances that video imagery with additional indicia that assists the rescuer  600  in more quickly retracing the steps of firefighter  300 . 
     Arrow  702  can be superimposed on the display by the video processor  520 , operating in conjunction with microprocessor  512 , which is configured to operate on the IMU data associated with the video data received from firefighter device  200 . That is, the IMU data associated with the video data indicates, among other things, direction of motion/travel with respect to, e.g., the direction of view of the camera  204  (using e.g., gyroscopes, accelerometers, and the like). In this way, the display can indicate to the rescuer  600  what the next step/direction of firefighter  300  was even though the firefighter  300  may have been looking in another direction. 
     The direction of arrow  702  can also be determined using the real-time IMU data received from IMU  506  of rescue device  500 . In this case, the real-time IMU data and the IMU data associated with the video data can be synchronized. For example, both sets of IMU data may contain an indication of direction using a compass heading. When both directions indicate, e.g., north, that means that the rescuer  600  is heading in the same direction as the firefighter  300  was heading. In such a case, the arrow  702  may point straight up signifying to the rescuer  600  that he is still following the direction of the firefighter  300   
     Another indicia that may be provided in accordance with the present invention is an indication that the firefighter  300  went through a door. Indicia  704  (“ENTER DOORWAY”) could be presented as highlighted or flashing text, and could be triggered as a result of the ultrasonic proximity detectors  310  detecting that the firefighter  300  passed through a doorway. Thus, again, the rescue device can be, in effect, “one step ahead” along the path  101  of firefighter  300  by providing additional indicia superimposed or overlaid on the video imagery provided on display  522 . In connection with doorway detection, the display  522  could also indicate how many doorways the firefighter  300  went through. Also, if the IMU  506  of the rescue device  500  includes ultrasonic sensors or other means of detecting doorways, then display  522  could include, e.g., a doorway counter that is decremented as the rescuer  600  passes through each doorway. 
     Another possible feature is that of elapsed time, shown in bar  720  at the base of display  522 . Bar  720  may include an indication of elapsed time of the video, e.g., 1 minute 37 seconds (1:37) and total length of video (2:07), along with current elapsed time (1:32). This can provide further information to the rescuer  600 , namely knowing that he should reach the firefighter  300  in about 30 seconds. This timing information also provides the rescuer  600  a sense of whether what the rescuer is seeing at the moment coincides with what the firefighter  300  was seeing after a given moment in time. This may give the rescuer  600  more confidence that he is in fact following the correct path to reach firefighter  300 . 
     Still another possible feature is that of an indication of a difference in speed between the firefighter  300  and the rescuer  600 . This speed difference can be calculated by microprocessor  512  and displayed on display  522 . 
     As further shown in  FIG. 7 , rescue device  500  may also include fast forward (FF)  706  and rewind (REW)  708  buttons, allowing rescuer  600  to fast forward or rewind the imagery being presented. Similarly, rescue device  500  may also include accelerate (ACC)  710  and decelerate (DEC)  712  buttons to control the speed at which the video imagery and associated indicia are played. For instance, it may be the case that the rescuer  600  is able to traverse the path  101  the firefighter  300  took much more quickly, and thus, the rescuer  600  need not necessarily follow the path at the same speed as the firefighter  300 . 
       FIG. 8  illustrates an example process that is performed in accordance with an embodiment of the present invention. At step  802 , video data is collected, recorded (stored) and streamed to a base station  400  or rescue device  500 . At substantially the same time, IMU data associated with the video data is collected, recorded and streamed to the same base station  400  or rescue device  500 . 
     At step  806 , the video data and IMU data associated with the video data are stored at the rescue device. At a later time, and at step  808 , the video data is played on a display of the rescue device  500 , and at step  810 , which occurs substantially simultaneously with step  808 , indicia are overlaid, superimposed or added next to the played video, where the indicia are indicative of, e.g., a direction of travel of a firefighter that took the video imagery, or a traversal path (e.g. through a doorway) of the firefighter  300 . 
     The foregoing disclosure of embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be obvious to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents.
Systems and methods for collecting and recording video data and inertial motion unit (IMU) data associated with the video data representative of a path of traversal, transmitting the video data and IMU data associated with the video data to a rescue device that includes a display, and subsequently replaying the video data on the display of the rescue device along with viewable indicia, based on the IMU data associated with the video data, that is indicative of the motion of a user when the video data was collected and recorded.