Abstract:
A method and apparatus that improves the positional accuracy of a geocoded point in comparison to traditional goecoding methods and geocoders. The method and apparatus utilize ground truth data (when available) in conjunction with address range information for a given segment to achieve positional accuracy not currently achievable in the prior art.

Description:
[0001]    This application claims priority to U.S. provisional application No. 60/815,836, filed on Jun. 23, 2006, which is hereby incorporated by references in its entirety. 
     
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to the field of geocoding and more particularly to a method and apparatus for geocoding with improved positional accuracy. 
       BACKGROUND OF THE INVENTION 
       [0003]    Geocoding involves programmatically assigning x and y coordinates (usually but not limited to, earth coordinates—i.e., latitude and longitude) to records, lists and files containing location information (full addresses, partial addresses, zip codes, census FIPS codes, etc.) for cartographic or any other form of spatial analysis or reference. Geocoding is even more broadly described as “mapping your data” in order to visualize information and explore relationships previously unavailable in strict database or spreadsheet analysis. 
         [0004]    A centroid is a geographic center of an entire area, region, boundary, etc. for which the specific geographic area covers. 
         [0005]    Street vectors are address segments of individual streets, which may contain attributes such as address ranges. Street vectors are used in displays of digitized computer-based street maps. Range information on street vectors is typically specified on the left and right side of each vector. They are also used for geocoding a particular address to a particular street segment based on its point along the line segment. 
         [0006]    Geocoding is currently performed by running non-geocoded (referred to hereafter as “raw data”) information such as a list of customers through proprietary software and/or data, which performs table lookup, fuzzy logic and address matching against an entire “library” of all known or available address points or street vectors (referred to hereafter as a “georeferenced library”) with associated x, y location coordinates. If the raw data matches a point record from the georeferenced library, then the raw data is assigned the same x, y coordinates associated with the matching record from the georeferenced library. If the raw data instead matches a street vector, then the raw data is assigned interpolated x,y coordinates pair based on the x,y coordinates of the high and low address for the matched street vector in the georeferenced library. 
         [0007]    The georeferenced library is compiled from a number of varied sources, depending on the territory, including census information, postal address information, street vectors with associated address ranges, postcode centroids and other various sources of data containing geographic information and/or location geometry. If a raw data address cannot be matched exactly to a specific library street address (known as a “street level hit”), then an attempt is made to match the raw data address to an ever decreasing precision geographic hierarchy of point, line or region geography until a predetermined tolerance for an acceptable match is met. The geographic hierarchy to which a raw data record is finally assigned is also known as the “geocoding precision.” Geocoding precision tells how closely the location assigned by the geocoding software matches the true location of the raw data. 
         [0008]      FIG. 1  illustrates a street segment called Main Street. The illustrated Main Street segment is for the odd side of Main Street and has an address range of 1 to 99 (odd numbers only) spanning between segment endpoints A and B. The coordinates of endpoint A are (X,Y) while the coordinates of endpoint B are (X 1 , Y 1 ). Heretofore, interpolation of input addresses in a geocoder was accomplished by considering the available high and low address range data in a georeferenced library for the given street segment and calculating where on that segment an input address from the raw data ought to reside based upon the latitude/longitude pairs of those two endpoints. 
         [0009]    For example, as illustrated in  FIG. 1 , given the Main Street segment, current interpolation methods will assume that addresses exist at points equidistant from each other and that the determination of where an input address from the raw data resides on a given segment is calculated using the coordinates of the segment endpoints A, B (or nodes) from the georeferenced library. Current interpolation will place an input address of 33 Main Street approximately one third (point C) of the way along the segment. 
         [0010]    The disadvantage of the prior art methods is that they fail to consider that houses, buildings, etc. are typically not located at regular intervals along a street vector or sometimes do not utilize the full range of possible address numbers assigned by the postal authority for the street vector. As such, these methods are not as accurate as they should be, which is undesirable. Users of such geocoding methods may assign locations to addresses on a street vector that are incorrect when compared to the actual ground truth positions of addresses on that street vector. For example, traditional interpolation can result in clustering addresses in close proximity at one end of a street vector when the actual addresses are distributed along a greater length of the street vector. In  FIG. 6A , the pushpins on the image depict the results of using a traditional interpolation technique to geocode addresses 2, 14 and 22 on Bieniek Ave, Adams, Ma., for which the postal authority has assigned the possible addresses of 1 through 99. In reality, the even-numbered addresses on the full length of the street, as indicated by the numbered stars, range only up to 22. Traditional interpolation methods assume the existence of addresses 2 through 98 on the even side of the street and therefore locate 2, 14 and 22 as being clustered on one end of the street, which in this instance is incorrect. Thus, use of the existing geocoding methods can result in errors in analysis and/or logistics where location is a key component. Accordingly, there is a desire and need for more accurate geocoding technique. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    Embodiments of the invention provide a method and apparatus that improves the positional accuracy of a geocoded point in comparison to traditional goecoding methods and geocoders. The method and apparatus disclosed herein utilize externally generated ground truth data (when available) in conjunction with address range information for a given segment (e.g., street segment) to achieve positional accuracy not currently obtainable in the prior art. The additional data is searched for and included in the interpolation methodology in a dynamic manner and in real time. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates interpolation of an address within a street segment according to conventional geocoding methods. 
           [0013]      FIG. 2  illustrates interpolation of an address within a street segment according to an embodiment of the invention. 
           [0014]      FIG. 3  illustrates a further interpolation of an address within a street segment according to an embodiment of the invention. 
           [0015]      FIG. 4  is a flowchart of a geocoding method of the invention. 
           [0016]      FIG. 5  illustrates a geocoder constructed in accordance with an embodiment of the invention. 
           [0017]      FIGS. 6A and 6B  illustrate the difference between interpolation results with prior art and interpolation with the current invention for addresses on a street segment in Adams, Ma. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    As set forth above, prior art geocoding methods fail to consider that houses, buildings, etc. are typically not constructed equidistant from each other. Nor do they consider the advent of point data files that are now becoming more available such as for example, point data via parcel centroid data or addresses located via GPS devices. To use this ground truth data optimally, a geocoder must be equipped to consume this additional data in a dynamic fashion, during run-time of the geocoding process, without requiring incremental modification of an underlying georeferenced address dictionary. To date, this has not been done. 
         [0019]    U.S. Pat. No. 6,101,496, assigned to MapInfo Corporation and incorporated herein by reference, considered the incorporation of different sources of street and/or address point information in the pre-processing of a native address dictionary upon which input addresses are geocoded. The &#39;496 patent, however, does not disclose or suggest a dynamic ability to consume and consider additional address information to pin point a location within a segment. 
         [0020]    The embodiments of the invention, on the other hand, allow users to introduce/input point data at any time. The point data, which is external to the native address dictionary, will be considered dynamically at run-time when input addresses are being assigned latitude/longitude coordinates during the interpolation process. This capability removes the need of the software vendor to extend the pre-generated georeferenced dictionary via additional processing. As such, the embodiments of the invention solve a long-felt need by allowing users to independently improve the quality of the geocoding process through their own efforts. 
         [0021]      FIG. 2  further illustrates the  FIG. 1  Main Street segment as interpolated in accordance with an embodiment of the invention. The illustrated Main Street segment is for the odd side of Main Street and has an address range of 1 to 99 (odd numbers only) spanning between segment endpoints A and B. The coordinates of endpoint A are (X,Y) while the coordinates of endpoint B are (X 1 , Y 1 ). Using the example above, a geocoder that can recognize and consider point data (such as e.g., parcel centroids or GPS-generated point files) within e.g., a pre-defined address dictionary, user dictionary or from any other external source, can improve upon the traditional interpolation method and generate a more accurate set of coordinates for the input address. 
         [0022]    Modifying the example described above, it is now assumed that the location of 17 Main Street is known (point D). The information regarding 17 Main Street may be housed in a pre-defined address dictionary, user-generated input dictionary, or it may be dynamically retrieved from another location (e.g., over the Internet or other connection to an external database). When the user requests the geocoder to locate the position of 33 Main Street, the geocoder of the invention determines a different set of coordinates from the prior art geocoder by interpolating between the closest known point with a house number less than 33 (which is 17 or point D) and the known point with a house number greater than 33 (which in this example is the endpoint B having address 99). Accordingly, as can be seen by comparing  FIG. 2  to  FIG. 1 , the positional accuracy for locating 33 Main Street (point C′) has greatly improved. 
         [0023]      FIG. 3  illustrates the results of the interpolation performed in accordance with the invention when an additional point E, having e.g., address 43 Main Street, is available in the pre-defined georeferenced dictionary or from any other external source. As illustrated in  FIG. 3 , the proposed interpolation can further refine the location of 33 Main Street by calculating the distance between 17 (point D) and 43 (point E) Main Street and determining where 33 Main Street (point C″) is most likely situated. 
         [0024]      FIG. 4  illustrates a method  100  according to an embodiment of the invention.  FIG. 5  illustrates an example embodiment of a geocoder  200  of the invention. The geocoder  200  comprises a computer or processor  202  having geocoding software capable of interpolating data from a variety of data sources and running the method  100  of  FIG. 4 . The sources illustrated in  FIG. 5  include a georeferenced address dictionary  206 , a user-supplied point data dictionary/database  208  and web-based sources of address point data  204 . The web-based sources of address point data  204  can include sources such as the Ordnance Survey in the United Kingdom, the Public Sector Mapping Agencies in Australia, or proprietary data warehouses developed and maintained by organizations and accessible only within those organizations. An example of the latter could be a utility company that establishes locations for its physical assets via GPS units. It should be appreciated that any source of address point data may be utilized and the invention is not to be limited to those illustrated in  FIG. 5 . The web-based and user supplied point data dictionaries/database  204 ,  208  will contain known data points and associated address information and coordinates for each data point. 
         [0025]    The method  100  begins by inputting an address to be geocoded (hereinafter the “input address”) at step  102 . At step  104 , the method  100  determines if a street vector match was found in the georeferenced address dictionary  206 . If a match was not found, the input address is compared to non-georeferenced postal data at step  114  and the method  100  completes. The result is the derivation of a latitude/longitude coordinate pair based upon a typically less geographically precise centroid rather than an interpolated street level “hit.” If at step  104 , it was determined that there was a street vector match, the method  100  continues at step  106  and captures the address ranges and associated coordinates from the matched street vector. At step  108 , a search is made for external point data associated with the matched street vector. The search includes querying the web-based and user-supplied sources of point data  204 ,  208 . 
         [0026]    At step  110 , the method  100  determines if external point data has been found. If external point data has not been found, the method  100  interpolates coordinates of the input address based on the address range coordinates associated with the matched street vector (step  116 ). If at step  110 , it was determined that there is external point data, the method  100  continues at step  112 , where the method  100  interpolates coordinates of the input address based upon the address range coordinates associated with the matched street vector and the externally discovered point locations. In a preferred embodiment, interpolation is performed by interpolating between the closest known point with an address less than the input address and the known point with an address greater than the input address (see e.g., the description regarding  FIGS. 2 and 3  above). After steps  112  and  116 , the method  100  terminates. 
         [0027]    It should be appreciated that the method  100  is implemented in software and may be stored on a computer readable storage medium such as a hard disk drive, floppy disk, CD-ROM, DVD and sold as an article of manufacture. The computer instructions implementing method  100  may also be stored on a network server and subsequently downloaded over a network to a computer system or other device/system. The computer instructions implementing the method  100  may also be programmed into various read only memory chips within or attached to the computer  202 , if desired. 
         [0028]    As described above, by using intermediate points on a street segment, input from a pre-defined geo-referenced address dictionary, user dictionary, or from other external sources, as opposed to solely considering the known endpoints of a given segment, the invention&#39;s interpolation of the derived location of an input address is a more accurate geographic representation of that address than other methods known in the art because it considers intermediate points whose ground truth is known and accepted as valid. This is evident by comparing the interpolation result shown in  FIG. 6A  (traditional) with the result illustrated in  FIG. 6B . The pushpins in  FIG. 6B  illustrate the vastly improved geocoded locations of the same addresses shown in  FIG. 6A , the improvement results from the method  100  performed in accordance with the invention. In addition, by including the availability of externally-sourced address point data, the embodiments of the invention further enable the interpolation methodology to be implemented in a dynamic fashion, consuming user-provided data as it is introduced at any time in the life cycle of the geocoding software. That is, the end result of the invention&#39;s geocoding process is an interpolated point that better approximates the ground truth position of the input address based on the combination of known endpoints for the matched street segment as well as the known location of other addresses associated with that segment. 
         [0029]    While the embodiments of the invention have been described in detail in connection with preferred embodiments known at the time, it should be readily understood that they are not so limited. Rather, the embodiments can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Accordingly, the embodiments of the invention are not limited by the foregoing description or drawings, but are only limited by the scope of the appended claims.