Abstract:
A mobile image capture system, a system comprising: a sensing unit for attaching to a vehicle, the sensing unit having a camera constructed and arranged to view a participant on the vehicle, the camera capturing at least one image; and processing electronics for storing data representing the captured at least one image or for relaying data representing the captured at least one image to a computer or a network.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/646,799 filed Dec. 28, 2006, which claims priority to divisional U.S. patent application Ser. No. 09/607,678 filed Jun. 30, 2000, now U.S. Pat. No. 7,739,076 issued Jun. 15, 2010, and to U.S. Provisional Patent Application No. 60/141,794 filed Jun. 30, 1999, and the contents of each of which is expressly incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to sports measurement sensors, event systems, and video systems; more particularly, the invention relates to various sports measurement metrics detected by sensors and relayed to an event system or personal display device and the production and use of video for spectator and/or training purposes. 
     BACKGROUND OF THE INVENTION 
     Sports participants, whether professional or amateur, as well as spectators desire more information about the performance of an athlete. United States patent application, entitled “Apparatus and Methods for Determining Loft Time and Speed,” U.S. Pat. No. 5,636,146, by Peter Flentov, Dennis M. Darcy, and Curtis A. Vock, assigned to PhatRat Technology, Inc., filed on Nov. 21, 1994, issued on Jun. 3, 1997, and incorporated herein by reference provides some systems and methods for quantifying airtime and speed for athletic performance, especially in the sports of skiing and snowboarding. 
     Patent Cooperation Treaty (PCT) Application, entitled “Sport Monitoring System for Determining Airtime, Speed, Power Absorbed and Other Factors Such as Drop Distance,” PCT Publication No. WO 98/54581, by Curtis A. Vock, Dennis M. Darcy, Andrew Bodkin, Perry Youngs, Adrian Larkin, Steven Finberg, Shawn Burke, and Charles Marshall, assigned to PhatRat Technology, Inc., filed on Jun. 2, 1998, published on Dec. 3, 1998, and incorporated herein by reference provides some additional systems and methods for quantifying athletic performance. 
     However, athletes and spectators desire new, quantifiable performance metrics, enhanced events systems, and use of visual images. For example, currently photographers can be found on the ski slopes at either the top or the bottom taking pictures, which can be later purchased at the end of the day from the Lodge. Whilst these are usually good quality photographs, they are not action images. Needed are new methods and apparatus to record a users performance from an action point of view as well as for other perspectives, and to distribute these recorded still and video images and video for entertainment and training purposes. 
     SUMMARY OF THE INVENTION 
     On embodiment of the invention includes a system comprising a sensing unit for attaching to a vehicle and processing electronics. The sensing unit has a camera constructed and arranged to view a participant or the vehicle, with the camera capturing at least one image. The processing electronics stores data representing the captured at least one image or relaying data representing the captured at least one image to a computer or a network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The appended claims set forth the features of the invention with particularity. The invention, together with its advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which: 
         FIG. 1A  is a diagram of one of many possible embodiments of a sports vehicle including a sensing unit and a camera; 
         FIG. 1B  is a diagram of a sports vehicle with a sensing unit built into a binding device for a user; 
         FIG. 1C  is a diagram of a camera; 
         FIG. 1D  is a block diagram of a sensing unit; 
         FIG. 1E  illustrates pseudo code for one embodiment for determining airtime; 
         FIG. 2A  is schematic diagram of an event system; 
         FIG. 2B  is a block diagram of a base station; 
         FIG. 2C  is a block diagram of a relay unit; 
         FIG. 2D  is a diagram of a half pipe event area and a vehicle; 
         FIG. 3A-B  are block diagrams of sensing units for measuring rotation and/or speed; 
         FIG. 4A-B  are flow diagrams for measuring rotation; and 
         FIGS. 5A-B  are block diagrams of a vehicle in the form of a baja race car and corresponding sensing device. 
     
    
    
     DETAILED DESCRIPTION 
     Methods and apparatus are disclosed for detecting and measuring performance characteristics and metrics of participants and vehicles. These performance characteristics and metrics include, but not are limited to, airtime, g-force, spin, rotation, drop distance, acceleration, and video and still images. These vehicles include, but are not limited to a snowboard, ski, skateboard, wakeboard, motorcycle, bicycle, ice skates and rollerblades. 
     One embodiment provides a camera for providing near real-time images and video footage of a participant&#39;s actions on a vehicle. The camera may be located on the participant, the participant&#39;s vehicle or other equipment, or from some other observation point. The images recorded by the camera can be downloaded to a recording or other storage device to produce memorabilia (e.g., a CD ROM, or video cassette). If desired, the images can be sent in real-time through an event system and network (e.g., using a radio or other transmitter) to television, the Internet, and to other locations for producing the memorabilia or for providing images to television display devices, such as those located in a ski lodge for entertainment purposes or in a coach&#39;s or personal trainer&#39;s office for training purposes. 
     For example, a camera may be attached to a snowboard or user for recording a user&#39;s performance. The camera should be easily but securely attached to the user&#39;s vehicle or body. Multiple cameras can be used to record multiple views simultaneously, such as a view of the user, a forward and a reverse view. The recorded images can be then be optionally digitally processed, and then recorded onto a compact disc for playback on the user&#39;s personal computer. 
     One embodiment provides a system that monitors and tracks vehicle action for teaching and training purposes. For example, a sensing unit (e.g., airtime sensor, etc.) may be attached to a skateboarder so that real-time and delayed data can be determined in a skateboarding training exercise or event. Further, a sensing unit and/or data unit may include one or more translational and/or rotational accelerometers to provide additional information such as, but not limited to, maximum rotation of the vehicle, rotation of the person relative to the vehicle, flip information, scraping information (e.g., one side of the vehicle relative to the other side of the vehicle), and a time duration that a vehicle is on its side or at an edge of a ramp. 
     Sensing units typically contain one or more transducers with suitable conditioning, filtering and conversion electronics. They typically also contain a processor, a data logging system and primary and secondary communication channels. Their purpose is to measure and record a parameter or range of parameters for a participant&#39;s performance and communicate the results to an event system or personal display device (e.g., watch, pager, cell phone, PDA, etc.). When sensing units are used in an event or resort/park situations, they typically transmit their results to a base station either directly or via a relay. For personal use, sensing units typically either transmit or display their results to a personal display unit integrated into the sensing unit or on a receiving device (e.g., watch, pager, cell phone, PDA, etc.). In one embodiment, the primary communication channel will typically be a one way radio frequency link or direct cable connection, which is used to transmit data to the rest of the system. A secondary bi-directional infrared link may be included, which allows administration and control of the sensing unit and also provides a path for the logged data to be downloaded. 
     One embodiment provides airtime and other information (e.g., performance metrics) related to Baja racing or other wheeled vehicles, in real-time, if desired, to television, event systems or judging centers, and/or the drivers of these vehicles. An embodiment uses a sensor that mounts to the vehicle in one or more places to monitor the airtime for one or multiple wheels. Various embodiments employ contact closures, stress sensing devices, accelerometers, and/or devices that measure the position of a shock absorber or coil spring for a wheel of the vehicle. 
       FIG. 1A  illustrates one embodiment of a vehicle  100 . As shown, vehicle  100  may correspond to a snowboard or wake board. However, vehicle  100  could also be any moving or sport vehicle, such as, but not limited to, a snowboard, ski, skateboard, wakeboard, motorcycle, bicycle, ice skates or rollerblades. Vehicle  100  could also be an animal, such as a horse. Vehicle  100  includes a sensing unit  102  and a camera  104 . Sensing unit  102  determines performance metrics or indicia thereof, which are typically stored within sensing unit  102  for later download and/or transmitted to a receiver system, such as one of the event systems described hereinafter. Camera  104  provides still and/or video action images of the participant or his performance. These images are typically stored within camera  104  for later download and/or immediate or delayed transmission to a receiver system, such as one of the event systems described hereinafter. If vehicle  100  corresponds to a snowboard for example, typically vehicle  100  includes a binding  101  for attaching vehicle  100  to a user. 
       FIG. 1B  illustrates one embodiment of a vehicle  110 . Vehicle  110  includes a binding (or boot) with an attached sensing unit  112 , as well as a camera  104  (previously described). By incorporating a sensing unit  112  having one or more pressure sensors, additional information such as power information and data relating to weight and balance techniques can be measured, stored, displayed and/or transmitted to an event or other receiver system. One pressure sensor suitable for use in a sensing unit  112  includes a peizo crystal or force sensing resistor. 
       FIG. 1C  illustrates a camera  120  which may be used to generate, record and transmit still or video images. In one embodiment, camera  120  comprises a processor  121 , memory  122 , storage devices  123 , a wireless interface  124 , a wired interface  125 , a charge coupled device (CCD) component  126  and optics  127 , battery  128  for supplying operating power to camera  120 , and one or more internal communications mechanisms  129  (shown as a bus for illustrative purposes). Wireless interface  124  and wired interface  125  receive and send external signals to one or more event systems or communications devices or networks (e.g., one or more networks, including, but not limited to the Internet, intranets, private or public telephone, cellular, wireless, satellite, cable, local area, metropolitan area and/or wide area networks). Memory  122  is one type of computer-readable medium, and typically comprises random access memory (RAM), read only memory (ROM), integrated circuits, and/or other memory components. Memory  122  typically stores computer-executable instructions to be executed by processor  121  and/or data which is manipulated by processor  121  for implementing functionality in accordance with certain embodiments described herein. Storage devices  123  are another type of computer-readable medium, and typically comprise disk drives, diskettes, networked services, tape drives, flash sticks, and other storage devices. Storage devices  123  typically store computer-executable instructions to be executed by processor  121  and/or data which is manipulated by processor  121  for implementing functionality in accordance with certain embodiments described herein. For example, in one embodiment, data corresponding to performance indicia or measurements are stored in memory  122  and/or storage devices  123 . Logging the image data in this manner allows for later processing, downloading and/or transmission. 
     As used herein, computer-readable medium is not limited to memory and storage devices; rather computer-readable medium is an extensible term including other storage and signaling mechanisms including interfaces and devices such as network interface cards and buffers therein, as well as any communications devices and signals received and transmitted, and other current and evolving technologies that a computerized system can interpret, receive, and/or transmit. 
       FIG. 1D  illustrates a sensing unit  130  which may be used to generate, record and transmit detected performance indicia and measured performance metrics. In one embodiment, sensing unit  130  comprises a processor  131 , memory  132 , storage devices  133 , a wireless interface  134 , sensing device(s)  135 , battery  136  for supplying operating power to sensing unit  130 , and one or more internal communications mechanisms  139  (shown as a bus for illustrative purposes). Wireless interface  134  sends, and optionally receives signals to one or more event systems or communications devices or networks (e.g., one or more networks, including, but not limited to the Internet, intranets, private or public telephone, cellular, wireless, satellite, cable, local area, metropolitan area and/or wide area networks). Memory  132  is one type of computer-readable medium, and typically comprises random access memory (RAM), read only memory (ROM), integrated circuits, and/or other memory components. Memory  132  typically stores computer-executable instructions to be executed by processor  131  and/or data which is manipulated by processor  131  for implementing functionality in accordance with certain embodiments described herein. Storage devices  133  are another type of computer-readable medium, and typically comprise disk drives, diskettes, networked services, tape drives, flash sticks, and other storage devices. Storage devices  133  typically store computer-executable instructions to be executed by processor  131  and/or data which is manipulated by processor  131  for implementing functionality in accordance with certain embodiments described herein. For example, in one embodiment, data corresponding to performance indicia or measurements are stored in memory  132  and/or storage devices  133 . By logging the data in this manner, performance parameters can be recorded for later processing and/or transmission. Moreover, these can be linked to video recordings to identify problem areas and leading to improvement in the user&#39;s performance. By way of example, performance data and video data may be downloaded to the Internet and data structures for later review or comparison of the user&#39;s data alone or with that of other athletes. 
     Sensing device(s)  135  may include accelerometers, stress sensors, magnetic field sensors, peizo foil sensors, pressure sensors, contact closures, global positioning system (GPS) devices, strain gauges, microphones, clocks, spectra, or any other sensing and/or measurement device. The exact device(s) incorporated into a sensing device  135  will typically correspond to the type of measurement desired. For example, magnetic field sensors and accelerometers, alone or in combination, can be used to measure rotation. 
     Each sensing unit  130  may contain a data logging data structure in memory  132  or storage devices  133 , which will be used to record the performance data generated by a competitor during a run. It typically will have sufficient capacity to hold the data for an entire run. This performance data stored in this data structure can be extracted at the end of each run. One embodiment of this data structure uses a FIFO principle; hence it will be self-maintaining and need not be interrogated should this be found inconvenient or unnecessary. 
     In the limited cases where data is lost during a competitors run then each sensors can be interrogated immediately on completion of that run. Live data collected by each sensor unit will normally be transmitted in real-time through an event system in order that judging can take place as the action is happening and also so that a live feed of performance information can be provided to TV or other medium, e.g., Internet or radio. Should a sensing unit  130  be unable to communicate through its primary communication channel then the accumulated performance data held by the sensors logging sub-system can be data can be download when the competitor has completed his/her run. This would take place using a secondary communication channel implemented with a different signaling technology. Typically, the primary communication channel with uni-directional (transmit only), the secondary channel will be bi-directional and used for downloading data from the logger sub-system and uploading one time pads. 
     Should the failure of a sensing unit  130  be more severe then unit can be open and the logging sub-system be downloaded directly. Each unit in the data chain will have the facility to download its data via secondary link using an alternative signaling system. In most case the units will be using radio frequency or RS232/RS485 as their primary medium of communication. In addition, a sensing unit  130  may have the capability to download its data via a secondary data link, such as infrared signaling. This would normally be carried out each time the a run has been completed. 
     Sensing units  130  typically transmit use a cyclic redundancy checksum (CRC) as part of a message so a relay unit or base station can detect a transmission error. In some embodiments, one or more error correction techniques (e.g., forward error correction) are used, which may allow corrupted data to be automatically corrected. A sensing unit  130  can use bi-directional communication techniques, but typically sensing units  130  only transmit their data in a datagram fashion, so no acknowledgement is received. Therefore, a sensing unit  130  will typically transmit each data packet several times to increase the probability of the message being properly received by an event system. 
     Many different methods are employed by a sensing unit  130  to determine a performance metric, such as airtime. In one embodiment, the sensor signal is filtered to give a cutoff frequency well below the Nyquist frequency for the sampling rate of 9600 Hz. The signal is typically sampled using an eight-bit analogue to digital converter. The 9600 bytes of information per second are preferably reduced to a more manageable level of 40 bytes per second by a pre-processing algorithm. The absolute difference of the current sample value from the previous sample value is, for example, accumulated for 240 values into a 16-bit number. Due to the high sample rate and the low frequency signal, the difference is always relatively small, and the 16-bit accumulator does not overflow. After 240 sample differences have been accumulated, the sum is divided by four and limited to 255. This value gives a ‘signal activity level’ for the 25 ms period. This technique effectively ignores low frequency signal content and any digital offset component. These values are fed into two Infinite Impulse Response (IIR) digital filters to determine if the vehicle is moving and if the vehicle is in the air. 
     Certain flags can be used in determining a performance metric. By way of example, the Motion IIR accumulator is 16-bits. The 8-bit signal activity level value is added in, and then the accumulator is reduced by 1/32nd of its current value. If the accumulator level is above a ‘Motion Threshold’, the vehicle is deemed to be in motion. The Air IIR accumulator is 16-bits. The 8-bit signal activity level value is added in, and then the accumulator is reduced by of its current value. If the accumulator level is below the ‘Air Threshold’, the vehicle is deemed to be in the air. A landing thump is flagged when the signal activity level is higher than the ‘Thump Threshold’. 
     The above flags are monitored and the following algorithm determines if airtime is valid. In one embodiment, the rules for valid airtime are straight forward: the board must be in motion before the airtime starts; the board may be in motion after the airtime ends; a maximum of 5 seconds of airtime is recognized (for a typical event or competition); valid airtime ends with a Thump (i.e., a landing). Pseudo code for one embodiment is illustrated in  FIG. 1E . While this may be a simplification of the full algorithm logic, it shows a basic mechanism for detection of airtime. The use of additional sensors will add additional qualifications to the algorithm transitions from Flying to Not Flying, and will reduce the number of airtimes detected incorrectly. 
     Certain embodiment employ certain enhancements, such as to help limit the effect of different signal levels on the algorithm outputs, the output value from the preprocessing can be limited to a certain value before being applied to the IIR filters. This limits the range of the filters, and restricts the effect of large signal inputs. 
     For certain events and embodiments, multiple sensing units  130  may be attached to participants and their vehicles. These multiple sensing units  130  may measure different performance metrics, or measure one or more of the same metrics as to provide some level of redundancy. 
     In one embodiment, sensing units  130  transmit a short block of data at relatively long intervals, for the remainder of the time the transmission band is free. By assigning different repeat patterns to each sensing unit  130  and repeating the same data a number of times then data loss due to overlapping messages can be virtually eliminated. In some embodiments, spread spectrum technology is used which typically provides higher reliability and security. 
     In one embodiment, each sensing unit and data link within an event system will facilitate or make use of encryption techniques to ensure the system cannot be subverted to the advantage of third parties such as competitors or gambling syndicates etc. The performance data in the system may be encrypted. In addition to, or in place of this encryption, Message Authentication Codes (MACs) may be included in the data streams. The MACs will accompany the data at all stages and locations within the event system including logging subsystems. The MACs will be used by a control center within an event system to establish the authenticity of any performance data received. In one embodiment, the performance data generated by a sensor unit within the event system will be grouped into blocks, a MAC will be generated for each block of data using that data. The MAC generation will be carried out by and within the sensor unit producing the data. The MAC will be an encrypted value derived from all the data within the block. 
     Additionally, in one embodiment, a system of One Time Pads (OTPs) is used to encrypt the Cyclic Redundancy Checksum (CRC) to generate the MAC instead of the processor intensive method common in standard encryption systems. Each byte of data within the data block will be used to generate the CRC for the block in addition a number of randomly selected bytes from the data block will be including in the CRC calculation a second time. This will prevent a third party from deriving the value of the entry of the OTP used to encrypt the CRC then using this information to generate a valid block of data and insert it into network without detection. Each entry in the OTP typically will consist of a pair of random numbers, one of the numbers will be used to select which data item are duplicated in the CRC, the other random number will be used to encrypt. This method allows a high level of data security while imposing a minimal processing burden where resources are at a premium. The OTP consists of a table of random numbers held in both the unit generating the data and the unit receiving the data. The table is unique to these two units and each entry in the table is only ever used once. 
     The rate at which MACs are included in the data stream, and hence the size of the data blocks, is determined by the amount of non-volatile storage available to hold the OTP and the frequency at which the OTP can be updated. It is not essential that the frequency of MACs is high. 
     Sensor units  130  may be uploaded with a unique and random OTP in a secure manner prior to each session the field unit might be used in. For this activity a single mobile security broker unit will be used this will generate a full set of OTPs for the entire event system for a session at an event. Each of the control units will be uploaded with a full set of OTPs. Once an OTP is loaded into a field unit and each of the control units it will be erased from the security brokers memory. 
       FIG. 2A  illustrates one embodiment of an event system used to receive information, typically in real-time, from the performance of an event.  FIG. 2A  illustrates a typical configuration used at a sporting event (e.g., a snowboard event) performed in event area  200  (e.g., a snowy hill). A series of n relay units  211 - 219 , where n is 0 or greater (0 meaning performance information is sent directly to base station  205 ), are used to receive transmitted performance information generated by a sensing unit (such as sensing unit  130  shown in  FIG. 1D ), which is relayed to a base station  205  for display on display and/or scoreboard  206 , processing, and/or retransmission to another location. Use of relay units  211 - 219  provides a reliable channel for the event data from the competitors as well as operational information for monitoring and provisioning the event system. Relay units  211 - 219  communicate with base station  205  via radio signals and/or cable  210  (e.g., using RS 485 protocol). 
     In certain embodiments, where radio links are used to transfer data between units, then a suitable transmitter and receiver beam shape will be employed to maximize link reliability. In the case of units in the relay array, a high gain directional antenna will be typically employed with the beam focused within the appropriate section of the event arena. In the case of repeater units, an Omni directional antenna will typically be employed. This embodiment should decrease the probability of a lost transmission even as the participant&#39;s orientation varies with respect to the event system. 
     In one embodiment, an array of m video cameras  221 - 229 , where m is 1 or greater, are placed along the event area  200  or at certain strategic locations (in addition to, or in place of relay units  211 - 219 ). Cameras  221 - 229  communicate with base station  205  via radio signals and/or cable  220  (e.g., using RS 485 protocol). Cameras  221 - 229  can be used to determine performance metrics, e.g., airtime, etc., by visually inspecting or digital processing the produced images. 
     The video cameras record events and then relay the events to a base station, which then might forward them to another device, such as a ski lodge video server so people in their rooms or in the lobby or bar can watch the action. In one embodiment, the event system automatically correlates participants having a sensing unit  130  ( FIG. 1D ) with recorded video by a video camera  221 - 229  based on a detected location of a sensing unit  130 . Typically, this location is determined by a radio reception signal strength at a relay unit  211 - 219 , or based on transmitted location by sensing unit  130  (e.g., when the sensing unit  130  includes a GPS sensing device). In one embodiment, the video camera is running continuously, which may be a boon for security of the park. Sensing unit  130 &#39;s transmission identifies the user by name, and supplies performance information to be combined with the video recordings. A computer system, such as base station  205 , can take the video clips and produce a ‘Days Best’ sequence of say 100 clips that play cyclically in the lodge. It can, for example, limit the number of clips of a single individual to his three best to give the rest of the participants a chance to get on the video board. The raw or combined video can then be recorded on CD for the paying customer or he can have only his individual shots (more than the three best limit) put onto the CD. 
     Moreover, performance data received from a sensing unit by an event system may be correlated with image data received by the event system. In one embodiment, data received from camera and sensing devices is time-stamped for later correlation and retrieval purposes, and/or marked with data identifying a participant or sensing unit. In one embodiment, the time value associated with at least some of the received performance or image data is adjusted based on a calculated, received, or some predetermined delay value. For example, a sensing unit or camera might add a relative delay time value to data it sends so the event system will be able to determine an “actual” time of occurrence. In this manner, events can be correlated based on a common time reference, such as that of the event system. In another embodiment, the clocks of sensing devices and cameras are routinely synchronized so that they can independently time-stamp data based on a common time reference, which will allow data received from different devices to be correlated. 
       FIG. 2B  illustrates a base station  240  which may be used to receive, display, and record and transmit detected performance indicia, measured performance metrics, and video and still images. In one embodiment, base station  240  comprises a processor  241 , memory  242 , storage devices  243 , a CD or DVD Read-Write Device  244 , external interface  245  for receiving information via radio signals, via a cable (e.g., using RS 485 or RS 432) or via some other device or communication mechanism, display interface  246  (e.g., for a monitor or scoreboard) and one or more internal communications mechanisms  249  (shown as a bus for illustrative purposes). Memory  242  is one type of computer-readable medium, and typically comprises random access memory (RAM), read only memory (ROM), integrated circuits, and/or other memory components. Memory  242  typically stores computer-executable instructions to be executed by processor  241  and/or data which is manipulated by processor  241  for implementing functionality in accordance with certain embodiments described herein. Storage devices  243  are another type of computer-readable medium, and typically comprise disk drives, diskettes, networked services, tape drives, flash sticks, and other storage devices. Storage devices  243  typically store computer-executable instructions to be executed by processor  241  and/or data which is manipulated by processor  241  for implementing functionality in accordance with certain embodiments described herein. For example, in one embodiment, data corresponding to performance indicia or measurements or video or still images are stored in memory  242  and/or storage devices  243 . 
       FIG. 2C  illustrates a relay unit  250  which may be used to receive, store and retransmit detected performance indicia, measured performance metrics, and video and still images. In one embodiment, relay unit  250  comprises a processor  251 , memory  252 , storage devices  253 , receiver  255  for receiving the information, transmitter  254  for retransmitting received data (and transmitting operations information) to base station  240  ( FIG. 2B ), and one or more internal communications mechanisms  259  (shown as a bus for illustrative purposes). Memory  252  is one type of computer-readable medium, and typically comprises random access memory (RAM), read only memory (ROM), integrated circuits, and/or other memory components. Memory  252  typically stores computer-executable instructions to be executed by processor  251  and/or data which is manipulated by processor  251  for implementing functionality in accordance with certain embodiments described herein. Storage devices  253  are another type of computer-readable medium, and typically comprise disk drives, diskettes, networked services, tape drives, flash sticks, and other storage devices. Storage devices  253  typically store computer-executable instructions to be executed by processor  251  and/or data which is manipulated by processor  251  for implementing functionality in accordance with certain embodiments described herein. For example, in one embodiment, data corresponding to performance indicia or measurements or video or still images are stored in memory  252  and/or storage devices  253 . 
       FIG. 2D  provides an example of one type of event area  200  (FIG.  2 A)—a half pipe event area  260 , such as that often used by skateboarders and snowboarders, along with a vehicle  261 . For this half pipe event area  260 , vehicles  261  will typically be equipped with sensing units  130  ( FIG. 1D ) that generate one or more of the following performance metrics: rotation/spin rate and quantity, tilt/leaning information, linear and/or rotational acceleration, speed, edge time and/or distance, drop distance, airtime, and experienced g-force. These performance metrics are typically relayed to either a personal display device or event system (e.g., that illustrated in  FIG. 2A ). 
       FIGS. 3A-B  illustrates embodiments  360  and  370  of a sensing unit  130  ( FIG. 1D ) for measuring rotation based on measured changes in a magnetic field, such as the Earth&#39;s magnetic field. Additionally, embodiments of sensing units  360  and  370  may measure movement of the sensing device through a magnetic field to determine a speed. 
     Sensing unit  360  typically includes a processor  361 , memory  362 , storage devices  363 , one or more magnetic field sensing devices  364 , and one or more external interfaces  365  (such as a display or a radio transmitter for communicating with an event system or personal display device). Sensing unit  370  typically includes a microchip PIC with memory  371  (or processor and memory), clock  372 , 3-axis magnetic field sensing device  374 , optional pitch and roll sensor  376 , one or more external interfaces  375  (such as a display or a radio transmitter for communicating with an event system or personal display device), and a battery source  377 . The operation of sensing unit  370  is further described by the flow diagrams of  FIGS. 4A-B . 
       FIG. 4A  is a flow diagram of one embodiment for determining a total rotation and rate of rotation. Processing begins with processing block  400 , and proceeds to processing block  405  where a total rotation variable is reset. Next, in processing block  410 , the current value of clock  372  ( FIG. 3B ) is recorded as the start time. Next, in processing block  415 , the first x, y, and z values of the 3-axis magnetic field sensing device  374  are recorded. After a delay (e.g., some number of microseconds) indicated by processing block  420 , the second x, y, and z values of the 3-axis magnetic field sensing device  374  are recorded in processing block  425 . Then, using the first and second recorded values and associated physics and mathematics, the rotational difference is determined in processing block  430 . If the determined rotational difference is less than some predetermined threshold (e.g., there is no more rotation) as determined in processing block  435 , then the rotational rate is determined in processing block  440 . Next, the rotational rate and/or total rotation are displayed or relayed to an event system in processing block  445 , with processing returning to processing block  405 . Otherwise, in processing block  450 , the total rotational difference is increased by the determined rotational difference. Then, the first values are replaced by the second values of x, y, and z in processing block  455 , and processing returns to processing block  420 . 
       FIG. 4B  is a flow diagram of another embodiment for determining a total rotation and rate of rotation. Processing begins with processing block  460 , and proceeds to processing block  462  where a total rotation variable is reset. Next, in processing block  464 , the current value of clock  372  ( FIG. 3B ) is recorded as the start time. Next, in processing block  466 , the first x, y, and z values of the 3-axis magnetic field sensing device  374  are recorded. After a delay (e.g., some number of microseconds) indicated by processing block  468 , the second x, y, and z values of the 3-axis magnetic field sensing device  374  are recorded in processing block  470 . Then, using the first and second recorded values and associated physics and mathematics, the rotational difference is determined in processing block  472 . Next, in processing block  474 , the total rotational difference is increased by the determined rotational difference. Then, the first values are replaced by the second values of x, y, and z, in processing block  476 . Then, as determined in processing block  478 , if the rotational amount and rate should be exported, then the rotational rate is determined in processing block  480 , and the rotational rate and/or total rotation are displayed or relayed to an event system in processing block  482 . Processing then returns to processing block  462 . 
       FIGS. 5A-B  illustrate another embodiment of a vehicle  500  and sensing unit  505  which may be used to provide airtime and other information (e.g., performance metrics) related to Baja racing or other wheeled vehicles, in real-time, if desired, to television or judging centers, event systems, personal display devices and/or the drivers of these vehicles. In this embodiment, vehicle  500  is a Baja motor vehicle. Sensing unit  505  is further illustrated in  FIG. 5B , in which a sensing device  525  is mounted to the vehicle in one or more places to monitor the airtime for one or all the wheels. Various embodiments of sensing device  525  employ contact closures, stress sensing devices, accelerometers, and/or devices that measure the position of a shock absorber  510  or coil spring  515  for a wheel  520  of the vehicle  500 . Sensing device  525  relays detected information over link  526  to the rest of the sensing unit (e.g., to a microchip PIC or processor) (or element  525  could be replaced by an entire sensing unit which relays data wirelessly, for example, to an event system or directly to a base station). 
     In view of the many possible embodiments to which the principles of our invention may be applied, it will be appreciated that the embodiments and aspects thereof described herein with respect to the drawings/figures are only illustrative and should not be taken as limiting the scope of the invention. To the contrary, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.