BULK FLOW LOCALIZATION AND IDENTIFICATION OF RFID-TAGGED ARTICLES TECHNICAL FIELD AND BACKGROUND OF THE INVENTION The present invention relates generally to an article handling system and method and, more particularly, to an article handling system and method that identifies and locates each article handled by the system. Article handling systems are configured to encompass a wide range of applications and, therefore, may be arranged in many different configurations. Article handling systems typically incorporate a number of different article manipulation devices in order to move and position the various articles being handled by the system. For example, conventional manipulation devices include singulators, inductors, and accumulators or the like, which may all be used to move and sort the articles to transform a typically disordered flow of articles into two or more sorted outgoing flows of articles. Articles are routinely routed to a particular exit based on their identification, such as a unique number or UPC code. Heretofore, the state of the art sortation systems first convert a disordered flow of articles into a singulated flow and, thereafter, barcode scan each article. An induction system then injects the articles into a sortation device, such as a shoe sorter, which directs the articles to appropriate exit chutes. Heretofore, the article identification occurs after the articles have been singulated. This is due to the fact that it is easier to scan and manipulate articles one by one rather than as a disordered dense stream of articles. For barcode scanning, a singulated well gapped and well defined parcel stream ensures a line of sight that is maintained for the proper scan of the articles. However, such systems are complicated requiring multiple components to achieve the sortation, which can be costly and, further, require a significant amount of space. Consequently, there is a need for a system that can process articles with fewer components resulting in a more economical, simpler, and, further, smaller system. SUMMARY Accordingly, the present invention provides an article handling system that facilitates the processing of the articles, particularly in a sortation system, and provides a simpler and smaller handling system, which saves cost, time, and space. The system and method uses radio frequency identifications, such as RFID tags, and benefits from the RFID tags' massive read parallelism by associating each RFID tag with its host parcel's location and geometric description. As a result, the present invention allows for the elimination of much downstream equipment found in conventional sortation systems, for example singulation beds, while enabling novel sortation architectures (both electromechanical and informational) which take advantage of early parcel identification. In one form of the invention, a method of handling articles includes conveying a plurality of articles in a bulk flow, each with a radio frequency identification, locating each article in the bulk flow in real-time using a vision system, and identifying the radio frequency identification of each article in the bulk flow, which is then associated with its location. The articles are then conveyed with their known locations and known identifications for further processing. In one aspect, each article is located by scanning each article using a camera. In a further aspect, each article is initially located by detecting the presence of the article using a detector, such as photo-eye array. In yet other aspects, each radio frequency identification is identified by reading each radio frequency identification of each article. In addition, a plurality of the radio frequency identifications may be read in parallel. According to another aspect, each article is located using a vision system that models each article. For example, each article is modeled by recovering or obtaining a two- dimensional or three-dimensional description of each article. Such dimensional descriptions may be recovered by scanning each article with a camera. In yet another aspect, the articles with known locations and known identifications are inducted into a sorter. For example, the articles with known locations and known identifications may be inducted into a carousel sorter. In another form of the invention, an article handling system includes a conveyor for conveying a plurality of articles in bulk, each with a radio frequency identification, a vision system, which scans an article to create an image of the article, at least one transceiver, and a controller. The transceiver is configured to generate a radio frequency signal to activate the radio frequency identifications of the articles and for receiving a radio frequency signal from the radio frequency identifications when activated. The controller is in communication with the vision system and the transceiver and is configured to associate the image of each article with its respective radio frequency identification and, further, locates each article based on the scanned-in images of the articles so that the controller may identify and locate each article in real time. In one form, the transceiver includes a transmitting antenna and a receiving antenna, with the transmitting antenna generating a radio frequency signal for activating the radio frequency identifications and with the receiving antenna receiving the signals from the actuated radio frequency identifications. In another aspect, the controller models each article based on a scanned image of each article, such as a 2D or 3D image of the article. In addition, each scanned image may include a scan of the radio frequency identification associated with the article being scanned. In another aspect, the receiving antenna comprises a plurality of antennas, such as antenna loops. For example, the antennas may be embedded in the conveyor. In yet another aspect, the transmitting antenna comprises a directional antenna. Further, the transmitting antenna may have a variable output power. According to another aspect, the receiving antenna may comprise two or more antennas. For example, the receiving antennas may be placed at fixed locations with the antennas being configured and arranged to form a substantially non-parallel collection of visible and invisible regions. According to yet another form of the invention, an article handling system includes a first conveying region for conveying a plurality of articles, a second conveying region, which defines a location and identification region, with the first conveying region for conveying the articles to the second conveying region, a third conveying region, and a location and identification system. The location and identification system locates and identifies each of the articles at the location and identification region, and the third conveying region conveys articles identified and located at the second conveying region from the second conveying region to a desired destination. In one aspect, the location and identification system includes a vision system and a radio frequency based identification system. In another aspect, the identification system includes a radio frequency identification transmit antenna and a radio frequency identification reader. For example, the transmit antenna may comprise an overhead antenna located above the second conveying region or may be remotely located relative to the second conveying region. In addition, the transmit antenna may comprise a transmit antenna with a variable output power, which may be particularly suitable for a remotely located antenna. In yet a further aspect, the radio frequency identification reader includes a plurality of antennas, such as antenna loops. For example, each antenna may allow for selection based on the local coverage for each antenna. In addition, the antenna loops may be embedded in the second conveying region. In yet another aspect, the vision system includes a vision device for scanning each of the articles at the location and identification region and for generating models, such as 2D or 3D models, of each of the articles from the scanned images. For example, a suitable vision device includes one or more digital cameras. The cameras are preferably arranged so that they scan the whole sensing area of the second conveying section, which may represent the whole conveying surface of the second conveying region or a portion of the conveying surface. For example, the cameras may be arranged along the central section of the conveyor along the conveying direction. Accordingly, the present invention provides a system and method of handling articles in a manner that is simpler and more cost effective than systems known heretofore. These and other objects, advantages, purposes, and features of the invention will become more apparent from the study of the following description taken in conjunction with the drawings. DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall layout of a sortation system incorporating a bulk flow localization and identification system of the present invention; FIG. IA is an enlarged schematic view of the localization and identification system of FIG. 1; FIG. IB is a flow chart of the process of localization and identification system of FIG. IA; FIG. 2 is a schematic drawing of the location and identification portion of the localization and identification system of FIG. IA illustrating the control system; FIG. 3 is another schematic drawing of the control system of the location and identification portion; FIG. 4 is a flow chart used by the controller of the location and identification process of the system; FIG. 5 is a schematic drawing illustrating another embodiment of the radio frequency identification system of the location and identification portion illustrated the use of a remote transmit antenna with a variable power output; FIG. 6 is a block diagram of the transmit and receiver antennas and the RFID reader of the radio frequency identification system of FIG. 5; FIG. 7 is a schematic drawing illustrating another embodiment of the radio frequency identification system using two receiver antennas to create receiving and non- receiving regions; FIGS 8-11 illustrate the various stages of articles in the sortation system of FIG. 1; FIG. 12 illustrates the present invention used in a pre-sorting system for a cross-docking facility; and FIG. 13 illustrates the localization and identification system of the present invention feeding into an induct system that feeds into a carousel sorter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and IA, the numeral 10 generally designates an article handling system of the present invention for use in a sortation system S. As will be more fully described below, and as best seen in FIG. IA, article handling system 10 is configured so that each of the articles in a bulk flow of articles (12), such as parcels, can be individually identified and located (14) so that they may be thereafter sorted (16) in a more efficient and less costly method than heretofore known. Referring to FIG. IA, system 10 includes a conveyor 18 with at least three regions or sections — a bulk flow region 20, a location and identification region 22, and a released location region 22 where the articles have been each identified and located. While generally illustrated as a single belt conveyor with three regions, it should be understood that conveyor 18 may be formed from three conveyor sections, with each conveyor section providing a respective conveying region. Further, conveyor 18 may be provided by a roller conveyor or roller conveyor sections or the like. Hence the term "conveyor" is used broadly to cover any assembly that provides a conveying surface. The first conveying region 20 — or bulk flow region — is where articles are conveyed in a random disordered flow. Each of the articles A in the region has been tagged with a radio frequency identification (RFID), such as an RFID tag T, preferably on the exterior surface of the article. Radio frequency identification systems, commonly known as RFID systems, are well known and typically include a transmitter antenna or coil, a transceiver with a decoder, and a transponder — an RFID tag or the like. When the transmitter antenna emits radio frequency signals, which are generated by the transceiver, the signals activate the RFID tag. When activated, the data on the tag is reflected back and received by the receiver antenna of the transceiver for subsequent processing. Conveying region 20 conveys articles 12 to second conveying region 22 where the articles are scanned, located, and identified by a location and identification system 32 (FIG. 2), which includes a vision system 34 and, further, a radio frequency identification system 36. After each of the articles is located and identified by system 32, conveying region 22 conveys the identified and located articles to third conveying section 24 where all of the articles have been identified and located in real time so that they can be processed, for example, by an inductor Sl for sorting by a sorter S2 (FIG. 1). As best seen in FIG. 2, location and identification system 32 includes a controller 38, which is in communication with, for example, inductor Sl and/or sorter S2, vision system 34, and radio frequency identification system 36. In addition, system 32 includes a fusion module 40, which provides an interface between vision system 34 and identification system 36 and controller 38. As will be more fully described below, module 40 combines geometry information collected by vision system 34 with the identification information (such as on a cm-level scale) collected by identification system 36 so that the two types of information can be associated to control the handling of the articles. Referring to again FIG. 3, vision system 34 includes a detector 42 for detecting when an article is conveyed to conveying region 22 from conveying region 20, a second detector 44 to detect when an article is conveyed from conveying region 22 to conveying region 24, where the articles are then further processed using the identification and location information collected at conveying region 22, and one or more imaging devices 46. In the illustrated embodiment, detector 42 comprises a photo-eye array. When an article is fed from conveying region 20 to conveying region 22, photo-eye array 42 will detect the leading edge of each of an article or articles as they are fed into region 22 and generate a signal, which is communicated to controller 38. Detector 44, for example, may comprise a pair of photo-eye sensors, which detect when an article or articles leave region 22. Similarly, when an article passes between sensors 44, sensors 44 generate a signal, which is communicated to controller 38. Alternately, controller 38 may monitor the status of both detectors 42 and 44 to determine when articles enter or exit region 22. Imaging device 46 typically comprise a camera 48, such as a digital camera, and more preferably a plurality of cameras that are distributed over a sensing area 22a of conveying region 22. For example, sensing area 22a may comprise the whole conveying surface of conveying region 22 or a portion of the conveying surface of conveying region 22. Optionally, devices 46 are spaced so that they span at appropriate resolution the whole sensing area (22a). Optionally, a pair of devices 46 may be placed at the entrance of sensing area 22a as a stereo pair. Alternately, devices 46 may be placed along a spine of the sensing area — that is along the central area extending through sensing area 22a in the flow direction (as indicated by the arrows in FIG. 2). In another embodiment, devices 46 may be located under a transparent, including a semi-transparent, conveying section of conveying region 22. Devices 46 collect image data from each article. For example, devices 46 may collect 2D (two dimensional) data, such as the articles' 2D outlines, for example, as polygons annotated by an optional package height, or 3D (three dimensional) data. Another option is to collect a partial 3D model of each article. The images collected by devices 46 are then communicated to module 40. It should be noted that the proposed method of identification and localization preferably occurs in 3D, i.e., the location of RFID tags and the shapes of each parcel are modeled in three dimensions. As vision system 34 recovers a full 3D description of articles, the tag locations are limited to a bounded surface, e.g., on one of the six surfaces of a rectangular parcel. This approach presents an added advantage of eliminating the need for residual RFIDs that may be included in the contents of the articles. In the illustrated embodiment, imaging device 46 comprises an overhead imaging device 46, whose scans or frames are sent in real time to a controller 38 via module 40, which includes image processing software, such as described in copending application for a vision-based singulator, Ser. No. 10/208,703, filed July 29, 2002, which is incorporated by reference in its entirety. Using the information from imaging devices 46, module 40 and controller 38 identify the location of each article on conveying section 22 and associate each article with its respective RFID, as will be more fully described below. In preferred form, imaging device 46 scans each article, which scanned images are then assembled into a three- dimensional image using standard imaging processing algorithms to yield traceable article positions and orientations. Referring to FIGS. 2 and 3, radio frequency identification system 36 includes at least one transmit or transmitting antenna 48 and a plurality of receiver or receiving antennas 50. Transmit antenna 48 generates a radio frequency signal to actuate the RFIDs, typically RFID tags, on the respective articles. When a radio frequency identification tag T passes through the electromagnetic radio signal wave generated by transmit antenna 48, the signal activates the tag. Data encoded in the tag is then reflected by a data signal and recovered by one of the receiver antennas 50. In the present application, the tags are actuated and read in bulk — in other words, multiple identifications are read in parallel. In the illustrated embodiment, antenna 48 comprises an overhead antenna 52. Further, antenna 48 is located near or above conveying region 22, though as described in reference to FIG. 5, antenna 48 may be located remotely. Antenna 48 optionally comprises a directional antenna and, further, may optionally comprise a variable power output antenna. Receiving antennas 50 may be also be overhead or in-plane, or positioned as loops 54 embedded in region 22, for example, under the conveying region belt, over which articles translate at a known constant speed (e.g., 0.5 m/s). The choice of embedded loops is preferred if RFID coupling is inductive (< 11 MHz); for electromagnetic coupling (as it is the trend in the industry, e.g., 900 MHz tags), directional antennas are preferred. Embedded antenna loops 54 allow for selection on a local coverage for each loop and the known positions thereof. The present invention is based on the concept of altering the RFID reading process so as to controllably select appropriate read areas over which reads are likely to occur. Referring to FIGS 1, 2, and 4, articles (12) pi, p2, ... pi, are fed in bulk (with many side-by-sides, at random orientations) to left-to-right moving conveyor 18. A set of cameras 48 is distributed over sensing area 22a of conveying region 22. Vision system 34 collects the image data from the cameras and translates that into a 2D (or 3D) description of the passing articles. The geometries produced by vision system 34 are then fed to fusion module 40. Transmit antenna 48 transmits a signal, which activates the RFIDs. Antennas 50, which are positioned near the flow of articles, produce signals in response to the signal from the RFIDs and feed the signals to an RFID reader 37, which collects ID's of the articles lying in the vicinity of one or more antennas. ID's collected around a specific antenna may be labeled by that antenna's position. The ensemble of ID's collected is fed as a list to the fusion module 40. The job of module 40 is to combine the geometry information coming from vision system 34 to the information coming from the RFID reader 37. While vision system 34 produces geometries whose identities are unknown, RFID reader 37 produces a list of unique identities dissociated from specific parcel locations. Module 40 then correlates the appearance and disappearance of reads as reported by RFID reader 37 to the entrance and departure of parcel geometries (as detected by detectors 42 and 44 as reported by vision system 34 from the expected reading ranges of individual receiver antennas). The output of the fusion module 40 is a list of identified and located articles. Each article geometry produced by vision system 34 is augmented by its corresponding identifier, matched from an output from RFID reader 37. This information is fed to controller 38 which can then compute controls for example to inductor Sl and/or sorter S2 or to a singulator-like belt array that will realize sortation from bulk. Throughout the process, articles are located and identified while still in bulk and the sortation controls can be computed at this stage as compared to a conventional system that singulates first, and then sorts later. As best seen in FIG. 4, module 40 may associate the location and identification information from systems 34 and 36 using a probabilty method or approach (58). For example, as soon as an RFID tag is reported as read by a given antenna (60), it is associated with a list of possibly matching parcel geometries (62), namely, only those whose outline is found to intersect with the (approximate) reading field of that antenna (the geometry of that field can be fixed or modulated in position or amplitude, refer to previous figures). As the ID is still reported as readable by the same antenna (64), the probability that each parcel might be its match is incremented by a heuristic amount (66), e.g., the amount of relative overlap of that parcel with the antenna's field. For example, a parcel completely enclosed in the antenna's field will increment by a full unit at every cycle. A parcel only lying 20% inside of the antenna will increment by 0.2, and so forth. This heuristic has found to be a good one since the tag may lie anywhere over the surface of a parcel (and indeed within its volume). Once the tag is no longer reported at that antenna's field, the algorithm reports the parcel in its associated list with the highest accumulated probability (68). In a variant of this algorithm, logic checks can be added in such a way that a parcel previously associated to a tag can no longer be associated to another tag. Another improvement is to smooth (over many sampling events) what is deemed as an entering and leaving event, as the border of antenna fields produce noisy measurements.

Referring to FIG. 5 and 6, for UHF-range RFID tags, antenna emission may not be not local. For example, in the illustrated embodiment, antenna 148 has a variable output power. By varying the output power of transmit antenna 148, only RFIDs falling within the associated iso-power level (illustrated by dotted lines 148a) become sufficiently energized to transmit their ID's back to a reader antenna. Different power levels sent to the transmit antenna allow for different coverage areas and RFIDs to be selected. Correspondence occurs over a period of time, as parcels move over the conveying region. The correspondence algorithm can then utilize analytical or empirical descriptions of each iso-power level curve (e.g. -3dB), so as to create (over time) high-probability associations between responding IDs and relevant parcels (e.g., whose geometric description intersects a given iso-power curve).

As best seen in FIG. 6, a voltage-controlled amplifier 148b governs the power sent to the transmit antenna 148 (shown as a right-hand circularly polarized helix). Receiver antenna 150 (shown with reverse polarization to reduce reflective noise) recovers the signals of those tags energized by the transmit antenna's (148) field. Referring to FIG. 7, another embodiment of the present invention which does not require power level changes is shown. In the illustrated embodiment, radio frequency identification system 236 includes at least two receiver antennas 250a and 250b. This configuration is suited for when modulation of output power is impractical (e.g., due to noise and/or reflection) and/or too slow. Antennas 250a and 250b are placed at fixed known locations, so as to form a substantially non-parallel collection of "visible" and "invisible" (shadow) regions. In the illustration, a triangular shadow region (R0) is shown. The instant at which a given article 12 enters (or leaves) the shadow region is associated with a unique "height" of the triangle, and can therefore be associated with a unique article being tracked at that height. Other shadow and active regions can be constructed with more antennas allowing for even higher-probability correspondence. As would be understood from those skilled in the art, the present invention therefore combines real-time vision with RFID read data with an article or object for both locating (i.e., geometrically describing with respect to a fixed frame, for example at cm resolutions) and identifying the located articles' IDs so that the articles can be routed to a particular destination based on their identification. Referring to FIGS. 8-11, the localization and identification system of the present invention may be used in a number of differently configured systems. For example, system 10 may be combined to convey articles with known identifications and locations to an array-based direct sorter 300, whose architecture is substantially similar to the vision-based singulator referenced above. In addition, as best seen in FIG. 12, sorter 300 may be used as a pre-sorter for a large cross-docking facility 400 or used as an identify-and-induct system 300' for a carousel sorter 500 (FIG. 13). One of the benefits is the economic savings of doing early identification as reflected in the elimination of downstream equipment for sortation pipelines of the prior art systems. While several forms of the invention have been shown and described, other forms will now be apparent to those skilled in the art. For example, while separate antennas for transmitting and receiving have been described in reference to the radio frequency identification system, it should be understood that the transmitter and receiver antennas may be provided by a single antenna. In addition, other uses for the present invention include planning processing steps (e.g., scheduling deliveries) while parcels are still in the bulk (for cross-docking/JIT systems) and generally enhancing the robustness of RFID readers, etc. Therefore, it will be understood that the embodiments shown in the drawings and described above are merely for illustrative purposes, and are not intended to limit the scope of the invention which is defined by the claims which follow as interpreted under the principles of patent law including the doctrine of equivalents.