Patent Publication Number: US-7215280-B1

Title: Satellite positioning system enabled media exposure

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/366,349, filed Mar. 2, 2006, which is a continuation of U.S. patent application Ser. No. 10/318,422, filed Dec. 11, 2002, now U.S. Pat. No. 7,038,619, issued May 2, 2006, which claims the benefit of U.S. Provisional Patent Application No. 60/345,908, filed Dec. 31, 2001, and U.S. Provisional Patent Application No. 60/427,904, filed Nov. 20, 2002, each of which applications is expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to assessing the effectiveness of media displays. More specifically, the present invention is directed toward tracking individuals and their exposures to media displays using a satellite positioning system enabled device and other methods. 
     BACKGROUND 
     The media industries (print, television, radio, on-line, outdoor, and indoor) are always interested in determining their audiences so as to better assess the value of the products they provide to advertisers and others. Given recent developments in the media industries, there has been a renewed interest in outdoor and indoor media displays. Unfortunately, until now there has been a lack of consensus and acceptance of a system and/or method of assessing the value of outdoor and indoor media displays (e.g., billboards, posters, kiosks, video kiosks, on-line kiosks, and other publicly viewable media displays). More specifically, in recent years, the publicly viewable media display industries have made significant progress in delivering their publicly viewable media displays. Unfortunately, the research industry that could provide exposure, frequency, and reach estimates has not kept pace with these developments. Accordingly, publicly viewable media display providers have not been able to take advantage of media-buying changes and thereby increase market share against other measured media (e.g., television, radio, and on-line). In fact, many potential clients do not even consider publicly displayed media as there is no reliable measurement system to gauge exposure to the public. 
     Accordingly, it would be an advantage to provide accurate measurements of exposure to public media displays in order to obtain exposure, reach and frequency statistics that can justify the value of such media displays. However, there are unique problems with media displays. Radio, TV, and on-line media have the ability to assure a one-to-one or at least a one-to-a limited number tracking of viewers. The very nature of publicly viewable media displays allows a variety of individuals to be viewing the same display at the same time. Furthermore, there may be many more “channels” of publicly viewable media displays available in a given geographic area than would be available over radio or television. 
     This increase in both viewers and publicly viewable media channels provides scalability issues. If every individual and every media display must be tracked, the cost of calculating accurate reach and frequency statistics may become prohibitive. Previous media display solutions have tried to provide such an unscalable many-to-many solution. One such previous system has tried to provide radios in vehicles that respond to radios on media displays. However to be effective, such a system requires radios on every media display in a given environment to give an accurate assessment. Leaving a radio off a particular media display would mean that media display has no chance of being assessed. Additionally, a substantial subset of individuals must carry radios responsive to the media display radios in order for this approach to be even marginally effective. 
     Another ineffective solution has been the use of consumer surveys. Consumer surveys are ineffective because such surveys change respondent behavior and are inherently inaccurate as respondents rarely remember all the media displays they were exposed to. As many media providers are well aware, some media displays can convey a message, and change a respondent&#39;s behavior, without the respondent actively recalling that they were exposed to the media display. 
     Other previous systems have involved tracking vehicles through various means. While vehicle tracking is marginally effective, it has the drawback of being less granular with regard to demographics. Over an extended period of time many vehicles will have different occupants having different demographics. It is difficult, if not impossible, to accurately reconstruct the demographics of every passenger and/or driver of a vehicle. Additionally, under ordinary circumstances, vehicles are not allowed in pedestrian-only areas, such as shopping malls and/or pedestrian thoroughfares. 
     Similar needs are found in other industries that are also interested in determining their audiences so as to better plan for placement of services and other assets. Until now there has been a similar lack of consensus and acceptance of a system and/or method of assessing the value of placement of services and other assets. 
     Accordingly, there is a need for an accurate system and/or method for tracking the exposure of demographically identified individuals to media displays. Such tracking should be operable over extended periods and should track individuals both indoors and outdoors. It is desirable that such a system and or method also be usable in other industries. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     Utilizing monitoring devices for generating data useful in determining the effectiveness of various locations for an intended purpose is disclosed. In one embodiment, the data produced by the monitoring devices is useful in determining the effectiveness of media displays. In this exemplary embodiment, the monitoring devices are distributed to a number of study respondents for carrying on the person of the respondents, whose demographics are known. The monitoring devices track the movements of the respondents. While various technologies may be used to track the movements of the monitoring devices and, thus, the respondents, preferably the monitoring device location tracking utilizes a satellite position system (“SPS”) such as the global positioning system (“GPS”) or differential global positioning system (“DGPS”). More specifically, those of ordinary skill in the art and others will appreciate from the following description that the present invention may utilize a variety of satellite and radio frequency location tracking systems (e.g., GPS, Galileo, DGPS, GLOSNASS, WAAS, OMEGA, LORAN, VOR, etc.). Collectively, such systems will be referred to as positioning systems, for ease of description. Regardless of the nature of the location tracking system, the movements of the respondent and monitoring device at some point coincide with the location of a number of media displays. Collecting geo data (movement data) from the monitoring devices and knowing the location of media displays makes it possible to determine which media displays respondents were exposed to. This information allows the effectiveness of the media displays to be rated based on reach and frequency. Reach is a measure of how many respondents were exposed to a media display, and frequency is a measure of the number of exposures (on average) per respondent. 
     If desired, the monitoring devices may be initialized with study specific data (e.g., geographic regions of a study, length of time of a study, device behavior profiles, specific indoor zones to be tracked, etc.). In addition to utilizing SPS tracking, which requires access to SPS signals in order to determine a location, some exemplary monitoring devices may also utilize radio frequency identification (“RFID”) signals as an additional aid in determining a respondent&#39;s location. Other possible location determining components may be used in these monitoring devices. Accelerometers, gyroscopes, inclinometers, barometers and compasses may in some embodiments augment the location and movement tracking capabilities of the monitoring devices. 
     The data gathered from the respondents may further be categorized by demographics to allow for more detailed understanding of the effectiveness of media displays. 
     The monitoring devices may be distributed to respondents in any one of a variety of different manners, such as by mailing the monitoring devices to the respondents or in some way using a common carrier and/or courier to have them delivered to the respondents. 
     The effectiveness of media displays may be determined using a post-processing server after geo data has been obtained from a plurality of data sources, i.e., monitoring devices. The geo data represents locations along the path of travel of at least one respondent. The locations are matched to the locations of media displays. The effectiveness of such media displays is determined based on the number of matches between geo data locations and media display locations. If desired, prior to such a determination, the geo data is analyzed and any erroneous data (e.g., out-of-tabulation data) is removed. The effectiveness of the media displays is then rated by determining the reach and frequency of the media displays. 
     The geo data may be enhanced with other data to enhance accuracy. Both complete and incomplete geo data can be enhanced with other data. One source of other data is a geographic information system (“GIS”) database. Geo data accuracy can be enhanced by GIS data by locating a respondent on an adjacent street when the geo data places the respondent near, but not on, the street, for example. Additionally, the geo data may be “groomed” by conventional location data grooming methods to further enhance accuracy. 
     The post-processing server may determine media display effectiveness by obtaining geo data specifying the locations traversed by a monitoring device and matching the monitoring device locations with a number of media display locations (e.g., by determining whether the monitoring device traversed within a threshold distance of a media display location). Matches between monitoring device locations and the media display locations establish that the respondent carrying the monitoring device was exposed to the media displays. The geo data may be obtained directly from the monitoring devices or in the alternative may be obtained from intermediary devices such as download servers that obtain the geo data from the monitoring devices. In addition to retrieving geo data describing the locations and movements of a respondent, in an exemplary embodiment of the present invention, device data is also gathered. The device data may be gathered directly from the monitoring devices themselves or, as noted above, through intermediary devices such as download servers. Device data may comprise monitoring devices diagnostic data, monitoring device status information, etc. 
     The geo data may be periodically stored (“geo data points”). For comparison purposes, lines between these geo data points may be calculated. The calculated lines may be straight lines. Alternatively, curved lines based on the progression of geo data points may be calculated. Additionally, the geo data points may be used to calculate movement speed, i.e., velocity. 
     The geo data may be groomed to increase its accuracy. Potential grooming methods include adding DGPS data to the geo data, merging partial geo data locations with known data, and/or ascribing additional geo data locations from known data. 
     The geo data may be analyzed to locate anomalous data (e.g., data in incorrect form and/or data describing a highly unlikely location, etc.). Anomalous geo data may be stored for subsequent processing. Subsequent processing of anomalous and non-anomalous geo data is used to determine confidence ratings for monitoring device locations, i.e., geo data points. 
     In addition to determining exposures, the reach and frequency of media displays may be categorized in accordance with the demographics of respondents. Also, processing the geo data may be processed to determine gross rating points (“GRPs”) and daily effective circulation ratings for each media display. 
     A survey of respondent&#39;s recall of media displays may be obtained and processed. Processing is such that a respondent&#39;s recall is collated to respondent&#39;s geo data. In addition to recall, if desired, a survey of a respondent&#39;s purchasing behavior may be obtained and processed. Again, processing is such that a respondent&#39;s purchases are collated in some manner with the respondent&#39;s geo data. Processed recall and purchasing surveys are useful in rating the effectiveness of media displays. 
     Information other than media display effectiveness for existing media displays may also be determined. For example, the potential effectiveness of a location that could have a media display may be determined. Such a determination can be made by post processing geo data specifying a plurality of locations traversed by a monitoring device in a geographic region in accordance with a target level of media display exposure and a budget. All potential locations that fall within the budget are then matched to the geo data locations to determine for each of the potential locations whether the monitoring device would have been exposed to a potential media display at each of the potential locations. The result determines which locations would have had the most exposure. Reach, frequency, GRPs, and daily effective circulation may be factored in when determining the optimal placement for a media display. 
     The geo data may be used for location usage planning without regard to media displays. First, geo data specifying locations that have been traversed by monitoring devices within a geographic region are determined. Next, desired traffic (e.g., movement) characteristics for a desired location are selected. The geo data locations are then examined to determine their traffic characteristics. The established traffic characteristics of the geo data locations and the desired traffic characteristics are compared to determine whether any of the geo data locations conform to the desired traffic characteristics. The geo data may include the locations along lines between geo data points to allow for the planning of retail locations, services, and the like. 
     The monitoring devices may operate periodically to obtain SPS data by determining which satellites are available, identifying at least some of the available satellites and storing data of at least some of the satellites along with a date and time. When SPS data is unavailable, the monitoring devices may reduce power usage. 
     In addition to including SPS location determination components, the monitoring devices may include other types of location determining components such as RF locating components (e.g., transponders, receivers, transmitters, RFID devices, etc.). 
     The monitoring devices may decrease power usage when a motion sensing component indicates that a threshold time has passed with no movement of the monitoring device. Preferably, such monitoring devices stop trying to acquire SPS and/or other location information as there is no need to continually acquire this information by immobile monitoring devices. One suitable motion sensing component is a trembler device. 
     The monitoring devices may determine a projected life of the monitoring device&#39;s power source and change the period of acquisition of SPS and/or other location data based on a projected life of the power source. Such a determination allows a device whose battery power is almost exhausted to continue acquiring useful information over a period of time (such as a study period) during which data is desired. 
     The monitoring devices may include additional location determining components such as a radio frequency (“RF”) location determining component. Suitable RF location determining components are RF transponders, transmitters, and/or receivers that can be used to either gather additional location information, or in the case of a transmitter to provide identification information to a receiver at a known location. Of course, additional non-RF location determining components also may be included in such embodiments. 
     As will be readily appreciated from the foregoing summary, new and improved method, systems, and computer-readable medium for providing enriched location based information and using the information to determine the effectiveness of media displays, potential media display locations, etc., are provided. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a block diagram of a system for monitoring publicly viewable media displays; 
         FIG. 2  is a block diagram of a monitoring device for tracking a respondent&#39;s movements; 
         FIG. 3  is a block diagram of a download server for receiving data from a monitoring device; 
         FIG. 4  is a block diagram of a post processing server for processing information received from download servers; 
         FIG. 5  is an overview flow diagram illustrating a monitoring routine resident in a monitoring device; 
         FIG. 6  is an overview flow diagram illustrating a device analysis subroutine suitable for use in  FIG. 5 ; 
         FIG. 7  is an overview flow diagram illustrating a movement analysis subroutine suitable for use in  FIG. 6 ; 
         FIG. 8  is an overview flow diagram illustrating a power saving subroutine suitable for use in  FIG. 6 ; 
         FIG. 9  is an overview flow diagram illustrating a battery-processing subroutine suitable for use in  FIG. 8 ; 
         FIG. 10  is an overview flow diagram illustrating a location determination subroutine suitable for use in  FIG. 5 ; 
         FIG. 11  is a diagram illustrating interactions between a monitoring device, a download server, and a post processing server for determining media display effectiveness statistics; 
         FIG. 12  is an overview flow diagram illustrating an initialization routine resident in a download server; 
         FIG. 13  is an overview flow diagram illustrating a monitoring device download routine resident on a download server; 
         FIG. 14  is an overview flow diagram illustrating a post processing routine resident on the post processing server for further processing information from monitoring devices and the download servers; 
         FIG. 15  is an overview flow diagram illustrating an accuracy enhancing geo data grooming subroutine suitable for use in  FIG. 14 ; 
         FIG. 16  is an overview flow diagram illustrating a location matching subroutine suitable for use in  FIG. 14 ; 
         FIG. 17  is an overview flow diagram illustrating a tabulation statistics subroutine suitable for use in  FIG. 14 ; 
         FIG. 18  is an overview flow diagram illustrating a media display rating subroutine suitable for use in  FIG. 14 ; 
         FIG. 19  is an overview flow diagram illustrating a recall and purchasing rating subroutine suitable for use in  FIG. 14 ; 
         FIG. 20  is an overflow diagram of a media planning rating subroutine suitable for use in  FIG. 14 ; 
         FIG. 21  is an overflow diagram of a non-media planning rating subroutine suitable for use in  FIG. 14 ; 
         FIG. 22  is an overview flow diagram illustrating a reach and frequency analysis subroutine suitable for use in  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description which follows is in terms of processes and symbolic representations of operations by conventional computing components, including processors, memory storage devices for the processor, connected input and output devices. These described processes and operations may utilize conventional computing components as well as more specialized components in a heterogeneous distributed computing environment, including remote file servers, computer servers, and memory storage devices. Each of these conventional distributed computing components may be accessible by a processor via a communication network. 
       FIG. 1  is a functional block diagram of a system  100  for determining the reach and frequency of a respondent&#39;s exposure to publicly viewable media displays. While the system  100  generally operates in a computing environment comprising individual computer systems, some of which may be interconnected over a network (such as the Internet, publicly switched telephone network, or others), it will be appreciated by those of ordinary skill in the art and others that the system  100  could equally function with a single standalone computer system. The system  100  shown in  FIG. 1  includes a monitoring device  200 , satellite positioning system (“SPS”) satellites  105 , a media display  150 , a download server  300 , a post processing server  400 , and a geographic information system (“GIS”) database  125 . It will be appreciated by those of ordinary skill in the art and others that a conventional GIS database  125  may reside in the post processing server  400  or may reside on a separate device. The monitoring device  200 , download server  300 , and post processing server  400  are further described below in relation to  FIGS. 2 ,  3  and  4 , respectively. Additionally, while for ease of illustration only one monitoring device  200 , one download server  300 , one post processing server  400 , and one media display  150  have been shown, it will be appreciated that many such devices and/or displays may be included in the system  100  or that the download server  300  and the post-processing server  400  may reside on the same device.  FIGS. 2 ,  3 , and  4  illustrate exemplary devices suitable for determining the exposure to and reach and frequency of media displays. The devices are only examples and are not intended to suggest any limitation as to the scope of use or functionality of the invention. Neither should the devices be interpreted as having any dependency requirement relating to any one or a combination of components illustrated in the examples. 
     To better illustrate the interaction of, and purposes for, the devices of  FIG. 1 , the following exemplary embodiment is presented. In this exemplary embodiment, using the devices of system  100 , the effectiveness of the multiple media displays  150  is rated using multiple monitoring devices  200 , the download server  300 , and the post processing server  400 . The monitoring devices  200  are distributed to a number of study respondents. Each respondent carries the monitoring devices, which, in turn, track the movements of the associated respondent. The movement of the respondents carrying the monitoring devices at some point result in the respondents being exposed to media displays  150 , i.e., the respondents reach positions in their movements where they can visually or audibly receive the information provided by the media displays. As the respondents move, the monitoring devices store the tracking data determined by the monitoring devices (“geo data”). The geo data collected by the monitoring devices is used to determine which media displays the respondent was exposed to by comparing the geo data with location data defining the location of the media display. More specifically, the monitoring devices  200 , in the embodiment of the invention illustrated in  FIG. 1 , download their geo data to one or more download servers  300 . The download servers  300  forward the downloaded geo data to the post-processing server  400 . The post processing server  400  processes the geo data using data from the GIS database as necessary and compares the processed geo data with data defining the location of the media displays  150  to determine the exposure of the respondents carrying the monitoring devices to the media displays. The effectiveness of the media displays is then rated by the post-processing server  400  determining the reach and frequency of the media displays. Reach is a measure of how many respondents were exposed to the media displays, and frequency is a measure of the number of exposures (on average) per respondent. 
     The invention is operable in numerous general purpose or special computing device environments or configurations other than the exemplary one shown in  FIG. 1 . Examples of well known computing devices, environments, and/or configurations that may be suitable for implementing the invention include, but are not limited to, personal computers, server computers, laptop devices, multiprocessor systems, microprocessor-based systems, network PCs, minicomputers, mainframe computers, and handheld computers operable as stand alone devices and in distributed computing environments. 
       FIG. 2  depicts several key components of an exemplary monitoring device  200 . Those of ordinary skill in the art and others will appreciate that the illustrated monitoring device  200  may include more or less components than those shown in  FIG. 2 . However, it is not necessary that all of these generally conventional components be shown in order to disclose a monitoring device suitable for practicing the present invention. It will also be appreciated by those of ordinary skill in the art and others that a monitoring device  200  suitable for practicing the invention may have many form factors, e.g., as a small device carried by an individual, a vehicle mounted device, an added component of another device, etc. As shown in  FIG. 2 , the monitoring device  200  includes an input/output (“I/O”) interface  230  for connecting to other devices (such as the download server  300 ). Those of ordinary skill in the art and others will appreciate that the I/O interface  230  includes the necessary circuitry for such a connection, and is also constructed for use with the protocols required by a particular implementation of the invention. 
     The illustrated monitoring device  200  also includes a processing unit  210 , a clock  225 , an RF location component  240 , a SPS interface  245 , a trembler  215 , a directional unit  235 , and a memory  250  all interconnected along with the I/O interface  230  via a bus  220 . The clock  225  provides time information to the monitoring device  200 . The RF location component  240  is an optional component that is responsive to radio signals. The RF location component may include a receiver for receiving location information from another RF device or a transmitter that broadcasts the location of the monitoring device. Alternatively, the transmitter could transmit a monitoring device identification code for receipt by RF receivers located proximate to the media display  150 . Still further, exemplary RF location components  240  include active or passive radio frequency identification (“RFID”) components and RF transponders as well as receivers and transmitters. 
     The SPS interface  245  is a component that is operative to receive and record SPS signals. More specifically, the SPS interface includes a SPS engine well known in the art that receives signals from SPS satellites, pseudolites or related devices and uses the signals to determine the location of the SPS engine and, thus, the device incorporating the SPS engine. SPS is a generic reference to any satellite/pseudolite based location determining system. 
     The trembler  215  is an optional motion sensing component that detects whether the device with which the trembler is associated, in this case a monitoring device, has been handled, jostled, or in some other manner moved. Tremblers  215  are useful for determining when a device has not moved for extended periods of time so that power saving measures can be enabled. 
     The directional unit  235  is an optional non-RF directional component that does not require outside broadcasts or signals to determine either position or movement in a direction. Some exemplary directional units include compasses, accelerometers, gyroscopes, barometers, altimeters, inclinometers, and the like. 
     The memory  250  generally comprises at least one of a random access memory (“RAM”), a read-only memory (“ROM”) and a permanent storage device, such as a flash memory (e.g., flash RAM), other non-volatile solid-state memory (i.e., EEPROMs, FPGAs, etc.), disk drive, tape drive, optical drive, floppy disk drive, or some combination thereof. The memory  250  stores an operating system  255 , a monitoring routine  500 , geographic location data (“geo data”)  260 , device data  265 , and a store of profile data  270 . Profile data  270  may include respondent demographic information, device operation requirements (location sampling speed, power expectancy, distance to indicate movement of device, etc.) and RFID zone locations (regions where RFID communications will be turned on to augment SPS data). It will be appreciated that these software components, particularly those that change from time to time, such as respondent demographic information, RFID zone information, etc., may be loaded from another device, such as a personal computer (not shown) or the download server  300  into the memory  250  of the monitoring device  200  via the I/O interface  230 . 
     Although an exemplary monitoring device  200  has been described that generally conforms to a conventional general purpose computing device, those of ordinary skill in the art and others will appreciate that the monitoring device  200  may take on a variety of other forms. Additionally, while some embodiments or the present invention provide for a monitoring device  200  that is operative in an outdoor environment, it will be appreciated by those of ordinary skill in the art and others that the monitoring device  200  is capable of operation a number of environments, including environments heretofore inhospitable to SPS monitoring. Thus, the invention should not be construed as limited to the form shown in  FIG. 2  with or without the optional components or to the environments described above. 
       FIG. 3  depicts several key components of an exemplary download server  300 . Those of ordinary skill in the art and others will appreciate that the download server  300  may include many more components than those shown in  FIG. 3 . For ease of illustration, many conventional components likely to be included in an actual download server  300 , such as a keyboard, on-off switch, etc. are not illustrated. It is not necessary that all of these generally conventional components be shown in order to disclose an enabling embodiment for practicing the present invention. The exemplary download server  300  shown in  FIG. 3  includes an I/O interface  330  for connecting to other devices (such as a monitoring device  200  or post processing server  400 ). Those of ordinary skill in the art and others will appreciate that the I/O interface  330  includes the necessary circuitry for such a connection, and is also constructed for use with the necessary protocols required by a specific embodiment of the invention. 
     The download server  300  also includes a processing unit  310 , an optional display  340  and a memory  350  all interconnected along with the I/O interface  330  via a bus  320 . The memory  350  generally comprises RAM, ROM and a permanent mass storage device, such as a disk drive, tape drive, optical drive, floppy disk drive, flash RAM, other non-volatile solid-state memory, or combination thereof. The memory  350  stores an operating system  355 , an initialization routine  1200 , a download routine  1300 , a respondent ID database  360 , a monitoring device database  365 , and monitoring device (“unit”) files  370 . It will be appreciated that these software components may be loaded from a computer-readable medium into memory  350  of the download server  300  using a drive mechanism (not shown) associated with the computer-readable medium, such as a floppy, tape, or DVD/CD-ROM drive or via the I/O interface  330 . 
     Although an exemplary download server  300  has been described that generally conforms to a conventional general purpose computing device, those of ordinary skill in the art and others will appreciate that the download server may take a variety of other forms, including, but not limited to, database servers configured for information processing. Thus, the download server should not be construed as limited to the form shown in  FIG. 3   
       FIG. 4  depicts several key components of an exemplary post processing server  400 . Those of ordinary skill in the art and others will appreciate that the post processing server  400  may include many more components than those shown in  FIG. 4 . For ease of illustration, many conventional components likely to be included in an actual processing server  400 , such as a keyboard, on-off switch, etc. are not illustrated. It is not necessary that all of these generally conventional components be shown in order to disclose an enabling embodiment for practicing the present invention. The exemplary post processing server  400  shown in  FIG. 4  includes an I/O interface  430  for connecting to other devices (such as a download server). Those of ordinary skill in the art and others will appreciate that the I/O interface  430  includes the necessary circuitry for such a connection, and is also constructed for use with the necessary protocols required by a specific embodiment of the invention. 
     The post processing server  400  also includes a processing unit  410 , an optional display  440  and a memory  450  all interconnected along with the I/O interface  430  via a bus  420 . The memory  450  generally comprises a RAM, a ROM, and a permanent mass storage device, such as a disk drive, tape drive, optical drive, floppy disk drive, flash RAM, other non-volatile solid-state memory, or combination thereof. The memory  450  stores an operating system  455 , a post processing routine  1400 , a respondent geo database  460 , a media location database  465 , and an augmented DGPS database  470 . It will be appreciated that these software components may be loaded from a computer-readable medium into memory  450  of the post processing server  400  using a drive mechanism (not shown) associated with the computer-readable medium, such as a floppy, tape or DVD/CD-ROM drive or via the I/O interface  430 . 
     Although an exemplary post processing server  400  has been described that generally conforms to a conventional general purpose computing device, those of ordinary skill in the art and others will appreciate that a post processing server  400  may take on a variety of other forms, including, but not limited to, database servers configured for information processing. Thus, the post processing server should not be construed as limited to the form shown in  FIG. 4 . 
     As illustrated in  FIGS. 1 ,  2 , and  11  (described below), the monitoring devices of the display media assessment system  100  are used to track demographically identified individuals (“respondents”). The tracking or geo data is used to determine the exposure of the respondents to various media displays. 
     A flow chart illustrating an exemplary monitoring routine  500  implemented by the monitoring devices  200  is shown in  FIG. 5 . Prior to starting monitoring, all necessary variable data, such as a respondent&#39;s demographic data, RF zone data, profile data, is downloaded to the monitoring device. 
     The monitoring routine  500  begins at block  501  and proceeds to block  503  where the monitoring device is initialized. Next, in block  505  the monitoring device&#39;s status as having just been turned on is logged. Exemplary information that may be logged at block  505  are the date, time, and location (if available) of the monitoring device  200 . Next, in block  510  the status (expired or not expired) of a watchdog timer is logged. Then in block  512  the watchdog timer is reset. While not necessary to all embodiments of the present invention, the watchdog timer is used to restore device function in the case of a crash or other error. The operation of the watchdog timer is discussed in greater detail below in connection with a device analysis subroutine  600  shown in  FIG. 6 . Processing next proceeds to the device analysis subroutine block  600 , where the monitoring device  200  is analyzed. After the device analysis subroutine  600  returns, processing proceeds to decision block  515  where a determination is made whether sufficient time has passed (as specified in the current profile data  270 ) to check for the current location of the monitoring device  200 . If it was determined that a location check should not be made, processing cycles back to the device analysis subroutine  600 , or in the alternative, may wait until a location check is desired/required. In any case, after it has been determined that a location check should be performed, processing continues to a geo data gathering subroutine  1000 . An exemplary geo data subroutine  1000  is illustrated in  FIG. 10  and described below. As will be better understood from the description below, the geo data gathering subroutine gathers data about the location of the monitoring device  200 . After the geo data gathering subroutine  1000  returns, processing continues to decision block  520 , where a determination is made whether the location of the monitoring device was found during the pass through the geo data gathering subroutine  1000 . If a location was not found, processing cycles back to the device analysis subroutine  600 . If, however, in decision block  520 , it was determined that a location was found, processing continues to block  525 , where the geo data is compressed. Those of ordinary skill in the art and others will appreciate that compressing data reduces memory requirements and may increase the power life of the monitoring device, as less power is needed to store a smaller amount of information. However, it will also be appreciated that compressing the geo data is an optional step that may be unnecessary if sufficient memory and power are available. Next, in block  530 , the geo data is stored for later retrieval. Processing then loops back to the reset watchdog timer block  512 . The monitoring routine  500  continues processing until interrupted by either turning off the monitoring device  200 , or the monitoring device  200  loses power. 
     In order to ensure the accuracy and reliability of the measurements at the monitoring device  200 , monitoring device analysis (block  600 ) is included to routinely assess the status of the monitoring device  200 . Such analysis not only provides greater confidence that the data produced by the monitoring device  200  is accurate, it also can be used to enhance the monitoring time and accuracy of the monitoring device  200  by prolonging the useful life of a power supply by controlling the frequency of data gathering which is determined by the selected device profile data  270 . 
     As noted above, the monitoring routine  500  may include an optional device analysis subroutine  600 .  FIG. 6  is an exemplary illustration of a suitable device analysis subroutine  600 . Subroutine  600  begins at block  601  and proceeds to a movement analysis subroutine block  700 . A suitable movement analysis subroutine  700  is illustrated in  FIG. 7  and described in detail below. Briefly, the movement analysis subroutine  700  determines whether the monitoring device has moved a certain distance from a previous location. Failure of the monitoring device to move indicates that a respondent has remained at a particular location for an extended period of time. Routine  600  then continues to a power saving subroutine  800 . A suitable power saving subroutine  800  is illustrated in  FIG. 8  and described in detail below. In general, the power saving subroutine  800  causes the monitoring device  200  to operate in a more efficient manner, while still taking into account the desired/anticipated monitoring functions that will be required of the monitoring device  200 . Next, in block  610 , a determination is made whether any anomalous device events have been detected. Anomalous device events are any unexpected/out-of-bounds values present in the device data. Any detected anomalous device events are then saved in block  615 . Next, in decision block  620 , a determination is made whether the watchdog timer has expired. The watchdog timer expires if it is not timely reset during cycles through the monitoring routine  500  ( FIG. 5 ) described above. Expiration of the watchdog timer is evidence of a catastrophic error in the monitoring device  200 . More specifically, as noted above and shown in  FIG. 5 , the loop in which the watchdog timer is reset is always cycling. Expiration of the watchdog timer indicates a failure of the monitoring routine  500  to cycle and, hence, the occurrence of a catastrophic error. In such a scenario, a complete “reboot” of the monitoring device  200  is desirable. In one exemplary embodiment of the invention, rebooting acts as a power cycling instruction to the device such that monitoring routine  500  restarts at block  501 . Note that in monitoring routine  500  at block  510 , the watchdog timer status is logged. Therefore, a reboot instruction (block  630 ) would be logged at block  510 . If, however, in decision block  620 , it was determined that the watchdog timer has not expired, processing continues to block  699 , where the device analysis subroutine returns to its calling routine. 
     As noted above, the data gathering operation of the monitoring device  200  can be enhanced by including a movement analysis subroutine  700 . An exemplary movement analysis subroutine is illustrated in  FIG. 7 . As described more fully below, the movement analysis subroutine determines whether the monitoring device  200  has moved a sufficient distance to warrant indicating that the monitoring device and thus a person using the monitoring device has moved to a new location. Analyzing the movement of the monitoring device makes it possible to determine dwell time (time spent at a particular location) so as to enhance the assessment of any media displays in the area that may have captured a respondent&#39;s attention. 
     The movement analysis subroutine  700  begins at block  701  and proceeds to block  705 , where a measure is made of the distance between a reference location and the current location of the monitoring device. The reference location is the last location that the monitoring device  200  was at that was sufficiently different from a previous reference location to warrant recording a new location. As discussed more fully below, the sufficiency determination is based on a threshold that can be set to different levels in accordance with the selected profile data  270 . It should be noted that when the monitoring device is first turned on there may not be a reference location. Therefore, the first location is always a reference location, as well as the current location. Next, in decision block  710 , a determination is made whether the distance from the reference location is above a threshold. This threshold may be a fixed threshold or an adaptive threshold. A fixed threshold distance is specified in the profile data  270 . 
     An adaptive threshold depends on factors other than just distance, such as the respondent&#39;s location and/or movement patterns and/or speed. For example, if the monitoring device determines that a respondent is moving at vehicle speeds (e.g., over 10 mph) the threshold distance may be increased (to indicate vehicle movement). Alternatively, if a respondent is in a pedestrian only area that is rich in media displays, the threshold distance may be lowered, to provide for a more granular determination of a respondent&#39;s exposure to media displays. Whether or not a pedestrian is located in an area rich in media displays is readily determined by storing information about such locations in memory and comparing the current location of the monitoring device to such locations. Like the fixed threshold distance, the selected profile data  270  contains movement parameters with which to set an adaptive threshold. 
     Returning to decision block  710 , if it was determined that the distance from the reference location was not above the threshold, processing continues to block  725 , where the ending time of the time spent at the reference location is updated with the current time. If, however, in decision block  710  it was determined that the distance was above a threshold, processing continues to block  715 , where a new location and time are recorded as geo data. Additionally, in block  720 , the new location is stored as the new reference location. In either case, after block  720  or block  725 , the movement analysis subroutine  700  proceeds to block  799 , and returns to the calling routine. 
     As noted above, preferably, the device analysis subroutine  600  ( FIG. 6 ) also includes a power saving subroutine  800 . Power savings is of significant value because power sources (batteries, fuel cells, capacitors and the like) make a contribution to the size and/or weight of a monitoring device  200 . Accordingly, a small power source is desirable yet a small power source usually means less power. The monitoring device offsets the lower of power resulting from the use of smaller power sources by more efficiently determining when to use more and when to use less power. A power saving subroutine  800  suitable for accomplishing this result is illustrated in  FIG. 8  and described next. 
     The power saving subroutine  800  begins at block  801  and proceeds to a battery processing subroutine block  900  (illustrated in  FIG. 9  and described below). After the battery processing subroutine  900  ends, the power savings subroutine  800  proceeds to block  810  and then block  815 , where a determination is made whether the current location is inside an RFID (radio frequency identification) zone. An RFID zone is a zone within which the monitoring device is within communication range of an RFID device, i.e., a device that transmits RF signals or receives RF signals. Whether the monitoring device is within an RFID zone can be determined by storing the location of such zones in the memory of the monitoring device and periodically comparing the current location of the monitoring device with the stored locations of such zones. The determination is made by periodically checking the device profile data  270  for any listed RFID zones. 
     If, in decision block  815 , it was found that the current location is inside an RFID zone, the optional RFID functionality of the monitoring device  200  is turned on in block  820 . If, however, in decision block  815  it was found that the current location is not inside an RFID zone, the optional RFID functionality of the monitoring device  200  is turned off at block  830 . If in decision block  815  a determination could not be made as to whether the current location is inside or outside an RFID zone, the status is unknown and the current RFID status is maintained in block  825 . Enabling the RFID functionality only when the monitoring device is located in zones that have been designated as RFID zones (in profile data  270 ) allows the monitoring device  200  to use less power. Less power is used because the RF location component  240  is not enabled when it is not needed (i.e., when the monitoring device is outside of RFID zones). Typical RFID zones will be areas with media displays, but with little or no SPS coverage (e.g., subway stations, malls, stadiums, etc.). In any case, after turning on, turning off, or maintaining the current RFID status, processing continues to block  835 , where a determination is made whether SPS signals are blocked. 
     Those of ordinary skill in the art and others will appreciate that while there are a plurality of SPS signal broadcasting devices (satellites, pseudolites, etc.), signals from these devices may be blocked on occasion. This is particularly common underground and within substantial buildings. If SPS signals are blocked, useful location (geo) data cannot be obtained. An adverse effect on the power source of a monitoring device will occur if the monitoring device  200  constantly attempts to reacquire SPS signals when in areas where such signals are blocked. Therefore, if in decision block  840  it is determined that SPS signals are blocked, in block  850  the monitoring device is instructed to use a less aggressive SPS signal acquisition profile. Less aggressive, may mean using a lower power signal acquisition method, or trying to acquire SPS signals less often, or trying to acquire SPS signals for shorter periods of time. If in decision block  840  it was found that SPS signals were not blocked, in block  845  the monitoring device  200  is instructed to use a more aggressive (e.g., more powerful signal acquisition method or more frequent checks for SPS signals or checks for longer periods of time per check) SPS signal acquisition profile. After block  845 , processing continues to block  899  where the power saving subroutine  800  returns to its calling routine. 
     If the monitoring device  200  was instructed in block  850  to use a less aggressive SPS signal acquisition profile, processing proceeds to decision block  855  where a test determines if a threshold time limit has passed. The time limit may be established by a predetermined number of calls to the power saving subroutine  800 , or after a predetermined period of time has passed. If the threshold time limit has passed, the power saving subroutine  800  proceeds to block  845  where a more aggressive SPS signal acquisition routine is instituted. In this regard, those of ordinary skill in the art and others will appreciate that a SPS signal may be temporarily blocked. The monitoring device  200  would be less accurate if required to permanently employ a less aggressive SPS signal acquisition profile once such a profile is initiated, hence the decision (block  855 ) to periodically change the profile back to more aggressive SPS signal acquisition. 
     If in decision block  855  it was determined that the threshold time limit has not passed, then in decision block  860  a further determination is made whether any movement of the monitoring device has occurred within a predetermined period of time. This determination is made by monitoring the output of the trembler  215  ( FIG. 2 ) to determine if the trembler detected movement within the predetermined period of time. The predetermined period of time is continued in the profile data. An exemplary range is 2–15 minutes. This range is merely meant as an example and not meant to limit the range of predetermined periods of time employed by actual embodiments of this invention. The trembler acts as an indicator of whether the monitoring device  200  is actually in use. If, for example, the monitoring device has been placed on a bedside table, indicating that the associated respondent is no longer exposed to media displays, it is more power efficient to adjust the monitoring device so that the monitoring device consumes less energy. Accordingly, if in decision block  860  movement is detected, processing continues to block  899  where the battery saving subroutine  800  returns to its calling routine. If, however, in decision block  860  it was determined that there has been no movement detected by the trembler within a threshold time, processing continues to block  865  where the monitoring device  200  is placed in a sleep mode until the trembler detects movement. After the trembler detects movement, processing cycles back to the battery processing subroutine  900 . 
     As will be readily understood by those skilled in the art and others, the monitoring device  200  is used by respondents over extended periods of time. Accordingly, it is desirable to continually assess whether there is sufficient battery (fuel cell, capacitor, etc.) power to keep the monitoring device  200  in operation for the anticipated duration of the study. Such battery assessment can be used to control power usage and, thus, extend the operation time of the monitoring device.  FIG. 9  is an exemplary illustration of a suitable battery processing subroutine  900  directed to accomplishing this result. 
     The battery processing subroutine  900  begins at block  901  and proceeds to block  905  where the device checks its anticipated battery usage requirements. Next in block  910 , the monitoring device  200  determines available battery power. After which, in decision block  915  a determination is made whether a different device profile is needed. This determination compares both the current battery power availability, the anticipated battery usage requirements, and the indicated profile for the current study of the monitoring device  200 . For example if the current level of battery power availability is below the anticipated usage requirements, a lower power profile may be substituted for the current profile. Conversely, a higher power profile may be substituted if a available battery power is greater than expected. For example, if the current study of the monitoring device is monitoring an urban area for a two-week period, the determination of whether a different device profile is needed will depend on current battery power availability and the anticipated battery usage requirements of the monitoring device  200  and whether it will be able to adequately provide location information within an urban environment for the remainder of its monitoring period. 
     If in decision block  915  it was determined that a different device profile is not required, the battery processing subroutine  900  proceeds to block  999  where it returns to its calling routine. If however, it was determined in decision bock  915  that a different device profile was needed, in block  920  a better device profile is determined. For example, if the thresholds that have been set for the movement analysis subroutine  700  have resulted in repeated location checks that do not indicate that a monitoring device has moved from a referenced location, a more power efficient profile that causes the monitoring device to make less frequent location checks is chosen. Alternatively, if the movement analysis subroutine  700  finds that the threshold distance is always exceeded, a profile that increases the threshold distance to try and capture a “flighty” respondent is chosen. Next, in block  925 , the profile of monitoring device  200  is changed and processing proceeds to block  999  where subroutine  900  returns to its calling routine. 
     Although an extensive analysis of the operation of the monitoring device  200  is desirable, such an analysis is not essential to embodiments of the invention. The main purpose is to accurately track respondents. As generally noted above, the monitoring device  200  achieves this result by continuously determining a respondent&#39;s location, i.e., the location of a person carrying or in some other way associated with a monitoring device, and periodically storing the results of the determination. Monitoring device location is determined using either just SPS or SPS in combination with RF. RF location may include an RF interrogator mounted in the monitoring device  200  for interrogating an RF transponder and/or an RF transmitter for transmitting identification data for receipt by RF receivers when a monitoring device is sufficiently close to a receiver associated with a media display. Thus, depending on implementation, RF location determination can be considered somewhat equivalent to SPS satellite location determination, particularly if the monitoring device  200  receives information from prepositioned RF transponders in a manner similar to the way the monitoring device receives information from satellites. In this regard, those of ordinary skill in the art and others will appreciate that there are technical differences between SPS satellites, pseudolites (RF devices that, while not satellites, broadcast SPS satellite-type information) and RF transponders. Because of the similarity and in order to avoid unnecessary duplication, for purposes of the location getting subroutine  1000 , all received location signals are referred to as satellite signals. This in no way is meant to limit the present invention to only utilizing satellites for determining location. 
     The location getting subroutine  1000  ( FIG. 10 ) begins at block  1001  and proceeds to block  1005  where it is determined if satellites are in view, i.e., if the monitoring device is receiving satellite signals. Then, in block  1010 , the satellites whose signals are being received are identified. Next, in decision block  1015 , a determination is made whether there are a sufficient number of satellites to obtain a location. One of ordinary skill in the art and others will appreciate that different implementations of the present invention will require a different number of satellites with which to provide suitably accurate location information. In general, conventional SPS engines require receiving signals from four or more satellites if an accurate location is to be determined. However, less than four satellite signals may be used if less accuracy is acceptable, or if there are additional known pieces of information (e.g., altitude, latitude or longitude). These additional pieces of information could come from other directional units  235  of a monitoring device  200 . RFID systems and pseudolite systems may rely on less than three signals and still provide suitably accurate location information. One RFID and pseudolite signal source may be sufficient if elevation information is not required. Similarly, a single satellite signal may be sufficient if combined with known data, such as GIS information obtained from the GIS database  125 . 
     If in decision block  1015  it was determined that signals from enough satellites (or other devices) are being received, in block  1020  the current location of the monitoring device  200  is computed and stored. Next, in block  1025  information identifying the satellites that were used to determine the current location are stored. Additionally, in block  1030 , the current date and time are stored. Optionally, in block  1035  other relevant data, such as satellite signal level, individual pseudo-ranges of satellites (raw signal), augmentation data (e.g. WAAS or Wide Area Augmentation System data) and carrier phase (phase of radio wave from satellite) is determined, i.e., detected. In block  1040 , the other relevant data is stored. Finally, in block  1099 , the current location is returned to the calling routine. If, however, in decision block  1015 , it was determined that not enough satellite signals were available, processing proceeds to block  1045  where information identifying the satellites that signals were received from are stored. Then in block  1050 , the date and time are stored. As an insufficient number of satellite signals were available to calculate a location, processing continues to block  1098  where an indication that no location was found is returned to the calling routine. Regardless of which path is followed, after the location or no location result is returned, the location getting subroutine  1000  returns to the calling routine. 
     The RF location component  240  of the present invention may be operative in a number of different manners. In one exemplary embodiment, the RF location component  240  “chirps” out a low power signal with an identification that is then identified by one or more receiving RF devices at or near media displays. The strength of the signal may be monitored by the receiving RF device, such that only a signal of sufficient strength indicates an exposure to the media display. In an alternate embodiment, media displays have RF devices that broadcast a low power chirp that identifies of their location, such that the monitoring device  200  is able to record locations even when a SPS signal is not present. Similarly, the strength of the broadcast is monitored by the monitoring device  200 , such that only a signal of sufficient strength indicates presence at a particular location (or is of such low power that any reception indicates presence at a particular location). In still another embodiment, the media displays have RF devices that broadcast a chirp or beacon of an identifier, such that the monitoring device  200  is then able to record identifiers of specific media displays. Again, the strength of the broadcast is monitored by the monitoring device  200 , such that only a signal of sufficient strength indicates presence at a particular location (or is of such low power that any reception indicates presence at a particular location). 
     The operation of the display media assessment system  100  ( FIG. 1 ) of the present invention will be better understood by reference to  FIG. 11 , which illustrates an exemplary sequence of interactions between devices of the system  100 . As noted above, the display media assessment system  100  illustrated in  FIG. 1  includes a monitoring device  200 , a download server  300  and a post processing server  400 . 
     Turning to  FIG. 11 , a media display assessment sequence is initiated when a monitoring device  200  receives initialization information  1105  from a download server  300  or other suitable device. As noted above, the initialization information or data may include respondent demographic data, RF zone data, profile data, etc. After the monitoring device  200  has been initialized, monitoring can begin. Monitoring may commence immediately or after a period of time. In any case, after the monitoring device is initialized, i.e., ready to gather geo data, the monitoring device analyzes itself  1110  and then proceeds to gather geo data  1115 . Geo data gathering continues until the geo gathering is interrupted due to power source wearing out or the monitoring device being instructed to stop gathering geo data (e.g., because an OFF key is enabled). After geo data gathering is complete, or at periodic intervals, gathered geo data is downloaded from the monitoring device  200  to a download server  300 . More specifically when the monitoring device  200  is ready to download, device data  1120  is first transferred from the monitoring device  200  to the download server  300 . The device data includes data gathered by the monitoring device  200  about itself (e.g., device diagnostic data, power consumption data, etc.). The download server  300  adds  1125  the download device data to any previously received device data. For example, if multiple monitoring devices  200  store device data, the download server  300  would gather all this information together. After the device data  1120  has been downloaded to the server, the monitoring device  200  downloads geo data  1130  to the download server  300 . The downloaded geo data is accumulated  1135 . Next, the monitoring device  200  and the download server  300  may engage in a bidirectional exchange of diagnostic data  1140 , i.e., the monitoring device receives and responds to specific diagnostic requests from the download server  300 . The download server  300  then analyzes the diagnostic data  1145 . 
     Preferably, data from multiple monitoring devices  200  is downloaded to the download server  300  in the manner described above. After downloading the device and geo data  1150  are downloaded from the download server  300  to the post processing server  400 , the post processing server  400  performs a plurality of functions. Initially the post processing server grooms  1155  the geo data to improve its accuracy. Next, the geo data is aggregated  1160  into queryable results. The aggregated geo data is further processed  1165  using information derived from the GIS database  125 . Locations in the processed geo data are then matched  1170  to known locations of publicly viewable media displays. Next, the post processing server generates in tabulation (“in-tab”) and out of tabulation (“out-of-tab”) statistics  1180  which are used to determine what information is accurate and should be preserved. In-tab data is data that is said to have come from an accurate source (e.g., a well-functioning monitoring device  200  and a cooperating respondent). Out-of-tab data is said to be unusable for some reason (such as from a malfunctioning monitoring device  200 , corrupted data, and/or an uncooperative respondent). The geo data and matched locations are then fixed  1185  to cover any out-of-tab data that has been removed. The fixed data is used to determine reach and frequency  1190  statistics for the media displays. The reach and frequency statistics are then used to provide rankings and gross impressions  1195  for the media displays. 
     As will be appreciated by those of ordinary skill in the art and others,  FIG. 11  illustrates one exemplary set of interactions between the devices of system  100 . It will also be appreciated by those of ordinary skill in the art and others that additional interactions and selections may be employed by actual embodiments of the invention. Additionally, it will be appreciated by those of ordinary skill in the art and others that the actions illustrated in  FIG. 11  may be performed in other orders, or may be combined. For example, geo data may be downloaded before device data to the download server  300 . Thus,  FIG. 11  and the foregoing description should be taken as illustrative, not limiting. 
     As illustrated in  FIGS. 1 ,  3  and  11 , the exemplary embodiment of the display media assessment system  100  described herein includes a download server  300  that is used to retrieve information from monitoring devices  200 . Additionally, the download server is operative to initialize monitoring devices  200 . A flowchart illustrating an exemplary device initialization routine  1200  and a data download routine  1300  formed in accordance with the present invention are shown in  FIGS. 12 and 13 , respectively, and described next. 
     The monitoring device initialization routine  1200  begins at block  1201  and proceeds to decision block  1205  where a determination is made whether the device to be initialized is a new device, or one that has been used previously. If it was found in decision block  1205  that a new monitoring device  200  is to be initialized, processing continues to block  1210  where new firmware is downloaded to the monitoring device  200 . If however in decision block  1205  it was determined that a previously initialized monitoring device  200  is to be initialized, processing continues to block  1220  where any device and/or geo data stored in memory is cleared. Regardless of whether a new device or a previously initialized monitoring device  200  is being initialized, processing continues to block  1215  where the monitoring device&#39;s  200  operation is tested, i.e., a series of operational tests not part of the present invention are performed. Next, in decision block  1225 , if any errors were detected when testing the operation of the monitoring device  200 , processing continues to block  1235  where the monitoring device  200  is flagged as defective, after which processing ends at block  1299 . If however in decision block  1225  it was determined that no errors were detected during the operational tests in decision block  1230 , a determination is made whether the power supply is sufficient for the monitoring device  200 . The sufficiency decision in decision block  1230  may be affected by known and/or projected parameters of how much power a monitoring device  200  may need in an upcoming study (as stored in profile data  270 ). For example, measurements of the voltage and temperature of a battery power source, can be used to determine an expected level of performance given known average power consumption of monitoring device  200 . Alternatively, a fixed voltage level at a particular temperature may be used as a threshold to determine sufficiency of a power supply, for example, 2.8 volts at 70 degrees Fahrenheit (room temperature). Voltage below this level would be regarded as indicating insufficient power. If in decision block  1230  it was determined that the power supply is sufficient, processing continues to block  1240  where the device is flagged as having enough power. Next, in block  1245 , study specific data is added to the profile data  270  of the monitoring device  200 . In one exemplary embodiment of the present invention, study specific data includes designated zones where RFID measurements are to be taken. Other types of study specific data may include listings of anticipated satellites that should be available, device profiles for determining a location in a metropolitan area, frequency of location inquiries, duration of study, anticipation of time spent indoors or outdoors, and/or end date and time of study. Next, in block  1299 , the initialization routine  1200  ends. If in decision block  1230  it was determined that the power supply was insufficient, then in block  1250  the monitoring device  200  is flagged as not having enough power and processing again ends at block  1299 . 
     Besides initializing the monitoring device  200 , as shown in  FIG. 11 , the download server also retrieves information from the monitoring device  200  after a study. This retrieval may be accomplished by any conventional way computing devices communicate with one another (wireless, wire connected, networked, telephone, etc.). 
     An exemplary download routine  1300  suitable for use by the download server  300  is illustrated in  FIG. 13 .  FIG. 13  begins at block  1301  and continues to block  1305  where geo data is retrieved from the monitoring device  200 . Next, in block  1310  device status data is retrieved from the monitoring device  200 . Processing then continues to block  1315  where supplemental device diagnostics are performed. As noted above with regard to  FIG. 11 , supplemental device diagnostics include communication with the monitoring device  200  to determine the current diagnostic status of the monitoring device. In decision block  1320  a determination is made whether any of the received geo data, device status data or the results of the supplemental device diagnostics resulted in anomalous data, data errors or an insufficiency of data. If so, the error or condition is flagged in block  1325  and the anomalous data errors or indication of insufficiency of data is saved to a designated location for further processing. After the anomalous data or data errors have been flagged, processing ends at block  1399 . If in decision block  1320  no data errors or insufficiencies were found processing cycles to block  1399  and ends. 
     As illustrated in  FIGS. 1 ,  4  and  11 , the exemplary embodiment of the media display assessment system  100  described herein includes a post processing server  400  that is used to process and assess the data retrieved from monitoring devices  200  by download servers  300 . A flowchart illustrating an exemplary post processing routine  1400  suitable for implementation by the post processing server  400  is shown in  FIG. 14 . The post processing routine  1400  begins at block  1401  and proceeds to block  1405  where data is retrieved and saved from any download servers storing downloaded information obtained from the monitoring devices  200 . After the data has been saved, then processing continues to subroutine block  1500  where the geo data is groomed. An exemplary routine for grooming geo data is illustrated in  FIG. 15  and described in detail below. After the geo data has been groomed, processing continues to block  1410  where geo data from multiple monitoring devices  200  is aggregated. In one exemplary embodiment, this aggregation entails combining geo data from multiple respondents in the same vicinity to improve knowledge about that area and satellite coverage. 
     Next, in block  1415 , the geo data is further processed with information obtained from the GIS database  125 . The GIS processing may be iterative in that multiple passes may further improve the accuracy of the geo data. Accordingly in decision block  1420  a determination is made whether the geo data can be further improved with GIS and if so, processing returns back to block  1415 . Processing with information obtained from the GIS database includes eliminating all possible ambiguous SPS location solutions that are not on roads/sidewalks at surface altitude. For example, if the wavefront from a SPS satellite intersects a road at only one location, processing using GIS database information determines that the monitoring device  200  is at that location on the road indicated by the information gathered from the GIS database  125 . Ambiguous SPS location solutions may further be reduced using data regarding the speed required to move from a previous known location to a new location. 
     When the geo data has been sufficiently optimized using the GIS database  125 , processing continues to subroutine block  1600  where locations of publicly viewable display media are matched to locations where the monitoring devices  200  have been. A suitable location matching subroutine  1600  is illustrated in  FIG. 16  and described in detail below. 
     Those of ordinary skill in the art and others will appreciate that while the location matching subroutine  1600  described below discusses matching monitoring devices locations to the locations of publicly viewable media displays, the location matching subroutine  1600  may also be used to match other types of locations. For example, the location matching subroutine  1600  may be used to match monitoring device locations to potential media display locations as well as other types of locations. 
     Next, in block  1425  the content of matched media displays is identified. In one exemplary embodiment, media content identification involves identifying which media displays were matched and then looking up what media content was displayed at the times the monitoring device and the display locations matched. Processing continues then to block  1430  where supplemental measures are added to the data being processed supplemental measures include, but are not limited to, size, angle, lighting, time of day, blocking objects, clutter, and position. Next, in decision block  1435  a determination is made whether the location matches should be refined given the additional information received with regard to existing location matches and the supplemental measures. Supplemental measures may change the threshold for exposure to media displays. For example, an unlighted billboard at night would have a much lower threshold of exposure than the same billboard during the daytime. Similarly, if a building partially blocks a media display from a particular angle, a supplemental measure noting this effect would lower the threshold of exposure at certain locations. If the added supplemental measures information refines the location matches, processing cycles back to subroutine  1600 . If on the other hand in decision block  1435  a determination is made that location matches do not need to be refined, processing continues to a tabulation (“tab”) analysis subroutine  1700 . As noted above, tab analysis is the determination of which data should remain as part of an accurate assessment of the exposure and reach and frequency of media displays. A suitable tab analysis subroutine  1700  is illustrated in  FIG. 17  and described in detail below. Processing then continues to a ratings subroutine. Four illustrative ratings subroutines  1800 ,  1900 ,  2000  and  2001  are illustrated in  FIGS. 18 ,  19 ,  20  and  21 , respectively, and described in detail below. After the ratings subroutines are completed the post processing routine  1400  ends at block  1499 . 
     As noted above, preferably, the geo data retrieved from monitoring devices  200  is refined in grooming subroutine  1500 , an example of which is illustrated in  FIG. 15 . More specifically, those of ordinary skill in the art and others will appreciate that geo data grooming may be accomplished in many ways. Subroutine  1500  merely illustrates an exemplary series of steps that form one type of geo data grooming. Subroutine  1500  begins at block  1501  and proceeds to block  1505  where DGPS data is added (possibly from the augmented DGPS database  470 ) to improve (augment) the geo data received from the monitoring devices. Next, in block  1510  any partial geo data (e.g., SPS data obtained using less than four satellites) is analyzed to see whether it fills any potential holes in routes determined from the augmented geo data. Next in block  1515 , confidence ratings are computed for individual geo data points. Those of ordinary skill in the art and others will appreciate that different confidence levels may be ascribed to geo data points depending on the strength of signals and/or length of time a monitoring device  200  was exposed to a satellite signal. The confidence levels are used to further refine the geo data and intermediate points where geo data may not have been recorded. Next in block  1520  the geo data is further augmented by ascribing geo data locations from known data. For example, if a geo data location is found at the entrance of a tunnel and at the exit from a tunnel over a relatively short period of time, predicted points within a tunnel (or urban canyon) can be ascribed to the monitoring device  200  to establish respondent exposure to a media display located in the tunnel. In block  1525 , any anomalous geo data is saved for potential further processing. Finally, in block  1599 , subroutine  1500  returns to its calling routine. 
     An exemplary location matching subroutine  1600  suitable for use by the post processing server  400  is illustrated in  FIG. 16  and described next. In order to determine whether a respondent was exposed (or at least had the opportunity to be exposed) to a media display, it is necessary to determine if the respondent was in the vicinity of the media display. Accordingly, location matching subroutine  1600  compares respondent locations determined by geo data to media display locations. Location matching begins at block  1601  and proceeds to looping block  1605  where for all location zones (e.g., zones where someone might be exposed to a media display), are tested for matching. In block  1610  the geo data is examined to detect all routes that cross the location zone at different times from a direction (or directions) of interest. As the respondent may be moving at different speeds, at a given distance and a given speed there would have not been enough time for an exposure at a particular distance. Accordingly, in one embodiment of the invention a respondent has been exposed to a small media display when walking within fifty feet of the display, but not exposed when driving by the media display at 35 mph. This may be determined by examining the geo data and the location of the media display in question Next, redundant zone entries are eliminated (block  1615 ). The redundant zone entries are only eliminated if they indicate repeated entry and exit from the zone, which would indicate a location respondent who is close to a zone boundary. The redundant entries elimination performed by block  1615  is to add hysteresis to counter redundant zone crossings introduced by a respondent&#39;s movement. Then in block  1620 , additional information such as the number of zone crossings and the speed of these crossings is saved. At looping block  1625 , processing loops back to  1605  unless all location zones have been processed, in which case the location matching subroutine  1600  returns to its calling routine at block  1699 . 
     Not all information gathered by a monitoring device  200  is always going to be useful information. Non-useful information should be removed from the study if it is determined that it was inaccurately obtained. The determination of what information is non-useful is known as tabulation or tab analysis. 
     An exemplary tab analysis subroutine  1700  is illustrated in  FIG. 17 . The tab analysis subroutine  1700  begins at block  1701  and proceeds to looping block  1705  where for each monitoring device&#39;s data (or at least each study of monitoring if more than one person used the same monitoring device) the following is performed. In decision block  1710 , a determination is made whether there were any device failures. This information is included in the stored anomalous data. Device failure may be indicated by an indication that a monitoring device was producing erratic results, or that watchdog timer events were logged. Any data from monitoring devices having a failure indication is removed from the aggregated data sample in block  1725 . Next, the aggregated data is expanded to cover the removed data in block  1730 . Those of ordinary skill in the art and others will appreciate that the aggregated data may not have to be expanded in all circumstances. 
     If in decision block  1710  it was determined that there were no device failures, processing continues to decision block  1715  where a determination is made whether an uncooperative person used the device. Those of ordinary skill in the art and others will appreciate that if a respondent takes a monitoring device  200  and simply leaves it on a nightstand during the study period any geo data gathered would not be indicative of the respondent&#39;s exposure to publicly viewable media displays (except in the unlikely event that the person did not leave the vicinity of their nightstand for the full study period). Such respondents are designated uncooperative. Other examples will also be apparent to those of ordinary skill in the art and others, such as respondents never turning on a device. Accordingly, if in decision block  1715  it was determined that an uncooperative respondent used the device, processing continues to block  1720  where the uncooperative person&#39;s data is saved. Storing this data allows the uncooperative respondent to be included in the results of the study should it later be determined that the respondent actually was cooperative and potentially for other reasons as well. Processing then would continue to block  1725  and proceed as before. If however in decision block  1715  it was determined that a cooperative person (e.g., someone who turned on the device and carried it during a study) used the device, then processing continues to looping block  1735 . Processing also proceeds to looping block  1735  after block  1730 . At looping block  1735  processing loops back to looping block  1705  unless all devices data have been iterated through, in which case processing continues to block  1799  where subroutine  1700  returns to its calling routine. 
     As noted above, a number of different rating subroutines may be employed by embodiments of the present invention. Those of ordinary skill in the art and others will appreciate that the geo data that is obtainable from the monitoring devices  200  may have applications other than strictly determining the exposure, reach and frequency of publicly viewable media displays. 
     In a first exemplary rating subroutine  1800  publicly viewable media displays are assessed with regard to exposure, reach and frequency. Subroutine  1800  begins at block  1801  and proceeds to reach and frequency processing subroutine  2200 . An exemplary reach and frequency processing subroutine  2200  is illustrated in  FIG. 22  and described below. Next, processing continues to block  1810  where gross rating points (“GRPs”) are also calculated based on the geo data. Next in block  1815  daily effective circulation ratings are determined based on the geo data The ratings are then returned to the calling routine in block  1899 . 
       FIG. 19  illustrates an exemplary ratings subroutine  1900  for rating respondent recall and purchases. Subroutine  1900  begins at block  1901  and proceeds to block  1905  where respondents of interest are selected. These respondents of interest may be individuals selected in an arbitrary or random manner, individuals who are part of a particular demographic group or groups, or who have been exposed to particular media displays. Next, in block  1910  a survey of respondents&#39; recall of media displays is processed to determine which media displays the respondents recall. Then, in block  1915  a survey of respondents&#39; purchasing behavior is processed. Next, in block  1920  these process survey results are tabulated to form recall and purchase ratings with regard to matched publicly viewable media displays. Routine  1900  then returns at block  1999  to its calling routine with the recall and purchase ratings. 
     The previous discussions and ratings described above relate to existing media displays. In contrast,  FIG. 20  illustrates an exemplary media display planning subroutine  2000  for rating locations for potential media displays. Media planning subroutine  2000  begins at block  2001  and proceeds to block  2005  where target reach, frequency, and budget information is selected. Next in block  2010  a set of locations for potential media displays is selected. Then a reach and frequency subroutine  2200  that determines the reach and frequency of each potential media display location is executed. An exemplary reach and frequency subroutine is illustrated in  FIG. 22  and described below. After reach and frequency for each of the potential media display locations has been determined, in block  2015 , the reach and frequency of each location is compared to the target reach and frequency previously selected. Next, in block  2020  the locations&#39; ratings are determined based on how closely they match the target reach and frequency. Media planning rating subroutine  2000  then ends at block  2099  returning the optimum location or locations and ratings of those locations to the calling routine. 
       FIG. 21  illustrates an exemplary non-media planning (e.g., road traffic analyses, real estate development, service placements, etc.) subroutine  2100 . The illustrated non-media planning subroutine  2100  begins at block  2101  and proceeds to block  2105  where desired traffic (either vehicle or pedestrian) characteristics are selected. Next, in looping block  2110  for all known locations and routes the following is performed. A current location and route is compared to the desired traffic characteristics to form a rating in block  2115 . Next in looping block  2120  processing loops back to  2110  unless all known locations and routes have already been iterated through in which case processing proceeds to block  2125 . In block  2125 , a determination is made of the optimally rated location(s) and/or route(s) in view of the desired traffic characteristics. Non-media planning rating subroutine  2100  then ends at block  2199  returning all optimal location(s) and/or route(s). 
       FIG. 22  illustrates an exemplary reach and frequency determination subroutine  2200 . The illustrated reach/frequency determination subroutine  2200  begins at block  2201  and proceeds to outer looping block  2205  where for all demographics the following is performed. First, at inner looping block  2210  for all locations the following is performed. At block  2215 , a determination is made of which respondents were exposed to a zone of interest (reach). Next in block  2220 , a determination is made of the average number of times a respondent is exposed to a zone of interest (frequency). Processing then continues to the inner looping block  2225  which returns to block  2210  unless all location zones have been iterated through in which case processing continues to demographic looping block  2230  which loops back to looping block  2205 . If all demographics have been looped through, then processing continues to block  2299  where the reach and frequency determination subroutine  2200  returns to its calling routine. 
     While the term demographics has been used to describe different types of respondents, it will be appreciated by those of ordinary skill in the art and others that sociographic and psychographic categorizations may also be used with the present invention. Accordingly, instead of categorizing respondents based on age, gender, economic level and educational background, it may be possible to categorize respondents in other categories (e.g., early adopter, yuppie, baby boomer, etc.). Thus, demographics should be understood with regard to the present invention to also include sociographic and psychographic categorizations. 
     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.