Abstract:
A method of recognizing an object in an image is provided using multi-sensor integration through conditionally optimal geo-scene generation and registration. At least two images, one of which is a conditionally optimum, ortho-rectified base image, are input and used to generate a geoscene using ground control points in a latitude-longitude geospatial domain. Georegistration of the geoscene produces a registered geoimage which may be output. A virtual geospatial information system database may be compiled from the georegistered images. A Virtual Transverse Mercator (VTM) projection is defined which allows processing of images falling on both sides of the equator or across traditional UTM boundaries. The georegistration process utilizes the union and the intersection of image pixels, and geooverlaying with interacting layers including geogrids and text layers, to define main body and background pixels to facilitate object recognition.

Description:
RELATED APPLICATIONS 
     The present application is a Continuation-in-Part of U.S. patent application Ser. No. 11/074,245 filed Mar. 7, 2005. The present application is related to copending U.S. patent application Ser. No. 10/412,954 filed Apr. 15, 2003; Ser. No. 10/623,089 filed Jul. 18, 2003; Ser. No. 11/158,520, filed Jun. 22, 2005; and to U.S. patent application Ser. No. 08/066,691, filed May 21, 1993, now issued as U.S. Pat. No. 5,631,970, all of which are included herein in their entirety by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to object recognition in an image and, more particularly to recognition of an object in an image by generating, geomasking, geoindexing, registering, measuring, and geo-3D-visualization and geofly-through geoscenes to integrate multi-sensor images. 
     BACKGROUND OF THE INVENTION 
     In pattern recognition and remote sensing, object recognition is typically performed by gradually accumulating evidence from various sensors and from components within individual sensors. The first approach is usually referred to as intra-sensor integration, whereas the latter is referred to as inter-sensor integration. Information extraction from multi-sensor images is usually a more difficult procedure than is information extraction from a single sensor image simply because multi-sensor images are almost never spatially registered. Thus, the first step to multi-sensor integration is typically to physically register the images as completely as possible. 
     Multi-sensor coverage of an area can be illustrated, for purposes of discussion, using the New River Inlet Quadrangle of North Carolina. The imagery of the finest resolution is Digital Orthophoto Quad (DOQ) or Digital Orthophoto Quarter Quad (DOQQ) imagery generated by the United States Geological Survey (USGS). DOQ or DOQQ imagery has a spatial resolution level of approximately one meter/pixel. Another image type similar to DOQ imagery is called controlled image base 5 meter (CIB-5) which typically has a spatial resolution level of approximately 5 meters/pixel. Both DOQ and CIB-5 images are referred to as ortho-rectified or orthoimages the entire image surface has a constant scale. 
     The IKONOS-2 satellite was launched in September 1999 and has been delivering commercial data since early 2000. IKONOS is the first of a new generation of high spatial resolution satellites. IKONOS data records four channels of multispectral data at 4 meter resolution and one panchromatic channel at 1 meter resolution. This means that IKONOS is the first commercial satellite to deliver near photographic, high resolution satellite imagery of terrain anywhere in the world. IKONOS data is collected as 11 bits per pixel (2048 gray tones). Bands, wavelengths, and resolutions of the IKONOS data are: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Panchromatic 
                 0.45-0.90 μm 
                 1 meter 
               
               
                   
                 Band 1 
                 0.45-0.53 μm (blue) 
                 4 meters 
               
               
                   
                 Band 2 
                 0.52-0.61 μm (green) 
                 4 meters 
               
               
                   
                 Band 3 
                 0.64-0.72 μm (red) 
                 4 meters 
               
               
                   
                 Band 4 
                 0.77-0.88 μm (near infra-red) 
                 4 meters 
               
               
                   
                   
               
             
          
         
       
     
     The spatial resolution of the IKONOS imagery of the New River Inlet area is between about 1.1 meter/pixel and 1.4 meter/pixel. Resolution of the pixels along the x-axis is different from the pixel resolution along the y-axis in the IKONOS imagery. That means that these pixels are rectangular, not square. 
     Coarser-resolution satellite imagery for the test area in addition to IKONOS includes SPOT pan with a resolution of about approximately 10 m/pixel, and LANDSAT™ (enhanced thematic mapper) a resolution level of about 30 m/pixel. Like IKONOS imagery, the SPOT pan and LANDSAT imagery of the test site both also contain rectangular pixels. 
     In image processing and remote sensing analyses, it is generally assumed that the shape of the pixels in the imagery under investigation is square. However, for the above-noted test site, only DOQ and CIB-5 have square pixels; the rest of the images have rectangular pixels. Since IKONOS, SPOT and LANDSAT images are much more popular than are DOQ and CIB-5 images, it is surprising that most remote sensing researchers the world over have assumed these satellite images have square pixels. In reality these square pixels have never existed in most circumstances since 1972 when the first LANDSAT (originally called Earth Resources Technological Satellite (ERTS)) satellite was launched. The multispectral scanner (MSS) imagery had a spatial resolution of about 80 meters/pixel. With an orbiting altitude of about 500 miles and a spatial resolution of 80 meters, there was little concern about whether the ERTS pixels were square or rectangular. 
     With the introduction of DOQ in the 1990s, however, square pixels at the resolution level of one meter/pixel were available. Not much later, IKONOS imagery became available. It was generally believed that IKONOS imagery had a spatial resolution of 1 meter/pixel in the panchromatic domain, and 4 meters/pixel in the multispectral domain. For the most part, image users have not considered the reality of the shape of the pixels of the IKONOS imagery. Most people observing the images assume that a square pixel is the norm, and that DOQ can provide such pixels. The existence of non-square pixels among dissimilar imagery types, however, is one of the critical reasons why mismatching exists among multi-sensor images. Therefore, the first step in multi-sensor integration is to understand the causes and effects of non-square pixels over the entire image surface. 
     Spatial mismatch among multispectral images may result from dissimilarities in their resolution levels, their location or translation, their depression angles, their orientations, and combinations of these factors. Conventional methods of image registration include ortho-rectification and a number of image warping approaches (for example, nearest neighbor and rubber sheeting methods) as well as variations of these methods. Such methods are known to those of skill in the art. 
     An ortho-rectified image has a constant scale over the entire image surface, both vertically and horizontally, as if it were a map. Thus, when all of the input images are ortho-rectified, each of them has a constant scale, and each column of the image is oriented toward the north. Under these conditions, multi-sensor image registration becomes an easy task, that of changing the scale of one image to match the scale of the other image. In addition, a common pixel must be located in each image which becomes the very NW corner pixel in each image. The problem of using ortho-rectification as a means of image registration stems from the fact that ortho-rectification by itself is a very complex process. Consequently, in many cases, it cannot be assumed that ortho-rectified imagery is a natural product of any particular sensing system. 
     From the most commonly-used image processing software, such as Earth Resources Data Analysis System (ERDAS) and the Environment for Visualization Images (ENVI), one can conclude that conventional image registration approaches are centered on manually locating a few control points in the to-be-registered imagery, and then selecting one of the methods provided by the software package used to perform image registration. ( ENVY User Guide , Research System, Inc. 1996 Edition, pp. 10-1 to 10-16). 
     In its simplest form, image registration begins with matching the selected control points (i.e., pixels). Once the control point pixels are relocated to match the identical control points in another image, all the rest of the pixels must somehow be moved to create one or more new images. The rules by which the pixels in each image to be registered are moved in this context constitute an image registration algorithm. While computational procedures for image registration are computerized, the steps that the image analyst must follow are usually both time-consuming and tedious. Moreover, (originally called Earth Resources Technological Satellite (ERTS)) the spectral values of the original scenes may become altered after image registration. 
     A comparative analysis between ortho-rectification and conventional image registration methods provided by commonly used image processing software reveals that the superiority of ortho-rectification lies in its ability to generalize over a very large geographic region. Conventional approaches using manually-selected control points at a localized region, on the other hand, are usually not generalizable beyond the area covered by the selected control points. This also means that in order to cover a large geographic area with repetitive actions of control point section, the conventional image registration process is labor intensive. While ortho-rectification is capable of generalizing over a very large geographic region for image registration, the process of ortho-rectification itself is so complex that it usually requires a thorough understanding of the camera model and, in addition, generally requires having digital elevation models of the terrain of the image. 
     While distinct objects on images from different sources, having different scales, depression angles, and/or orientations, possess identical geospatial (i.e., latitude and longitude or “lat-long”) coordinates, geospatial information is not heavily utilized by conventional image registration approaches. On a flat map, one of the most commonly used counterparts of the lat-long system is the map-based Universal Transverse Mercator (UTM) projection that denotes a particular location using “easting” (in meters) and “northing” (in meters) plus a zone ID. Each UTM zone is defined by 6 degrees in Easting and 8 degrees in Northing. One degree represents about 110,000 meters. 
     This zone ID-based UTM system works well for point locations since one point location can be easily identified within one particular UTM zone. In an image that covers a large geographic area, the image pixels may fall into two different UTM zones. A case in point is the city of Culpepper, Va., which falls into two UTM zones. That is, East Culpepper DOQQ belongs to UTM zone  18 , whereas West Culpepper DOQQ belongs to UTM zone  17 . Since the central meridian for UTM zone  17  is different from the central meridian of zone  18 , there is a mismatch between the West Culpepper DOQ and the East Culpepper DOQ at the junction of these two DOQs. This mismatch occurs in center of the city. 
       FIG. 1  clearly shows the mismatch pattern at the junction of two UTM zones. As may readily be seen, one easily-seen feature appears twice, once in each of the UTM zones. Such an occurrence indicates a severe mismatch, at least in the upper region of the images.  FIG. 14  shows that possible mismatch due to dissimilar image orientations between two neighboring UTM zones may also exist in digital elevation model (DEM) data that represent the elevation readings of the terrain. Such data may also be denoted as “object height” data. 
     In this cross-zone scenario ( FIGS. 1 and 14 ), the mathematics used for the conventional UTM system may be inadequate to deal with the pixels in one image, which spans two UTM zones. Similarly, UTM has difficulty dealing with image pixels that are dispersed into both north side and south side of the equator. 
     Therefore, it is advantageous to define a way to measure the degree to which a given scene departs from an ortho-photo setting. In an ortho-rectified scene, it is necessary only to know one control point and to have the resolution of the pixel in order to determine the distance from a particular pixel location to another pixel location. 
     It is also advantageous to convert a given scene into a geoscene so that a distinct object in multiple images can possess the same geo-locational values, and the distance between two pixels or ground objects can be measured in terms of the earth&#39;s coordinate system, rather than in pixels. Similar methods may be used to quantify areas in images (i.e., to geomasking). In the method of the present invention, a pixel in a geoscene has quintuple representations:
         (1) (x,y) coordinates in the image domain;   (2) (z) coordinate in the spectral and/or elevation/height domains   (3) UTM representation in the geospatial domain;   (4) latitude-longitude in the geospatial domain; and   (5) Virtual Transverse Mercator (VTM) representation in the geospatial domain.       

     UTM is a map-based representation of latitude and longitude (lat-long) readings. Conversion between lat-long and the UTM system may be obtained using the methods outlined in Wolf and Ghilani,  Elementary Surveying: An Introduction To Geomatics  (Prentice Hall, 2002). Using the geoscene in accordance with the present invention, pixel (x,y) readings may be converted to UTM or the lat-long equivalent freely in both directions. This means that the distance between two pixels in the geoscene may be measured in terms of the physical distance in meters, on the ground. 
     Since image pixels may be distributed over multiple UTM zones and/or over both the north and south sides of the equator, it is advantageous to develop a modified UTM system by which the central meridian may be adjusted according to the spatial locations of the pixels instead of fixed locations. Also, the northing readings may be calculated across the equator in a continuous fashion. In the present invention, this is referred to as a Virtual Transverse Mercator (VTM) projection. 
     It is also advantageous to measure the resolution of a pixel in an image in terms of both x and y axes, or easting and northing in the context of both the UTM and the VTM systems. In the ortho-photo case, the x-resolution equals the y-resolution. In non-ortho-photo cases, however, the x-resolution does not equal the y-resolution. 
     It is advantageous to determine whether using only the x-resolution and the y-resolution information of two images is adequate to perform scene registration. 
     It is also advantageous to measure the degree of mismatch that still exists between two scenes by using two control points after the condition of rectangular, non-square pixels are accommodated. 
     Since the use of rectangular pixels cannot account for all the factors affecting mismatch between two scenes, it is advantageous to develop a method by which two general scenes can be registered by using multiple (e.g., four) control points. 
     It is equally advantageous to develop an image registration method by which the spectral values of the pixels in the original inputs are not altered after registration. This is important because the spectral signature of a given object is based on the original spectral values of the pixel representing that object. Any deviation from the original spectral value may create errors in subsequent object recognition. Such errors in the DEM domain are intolerable since a change in the terrain elevation due to image processing error can potentially result in severe consequences. 
     It is also advantageous to develop a new image registration method by which, after image registration, the spectral value of a given pixel at a given image location or geo-location will not be influenced by the spectral value of any neighboring pixel. 
     It is definitely advantageous to perform a near-perfect ortho-rectification for image registration without having to use a camera model of the sensor and/or the digital elevation data of the imaged area. 
     It is also advantageous to perform both image registration and image mosaicking simultaneously when multiple images align correctly in the geospatial domain. 
     It is also advantageous to define the region of intersecting and unioning in terms of a geomask supplied by an independent source, such as a user or a detector. This process is called “geomasking”. The result of geomasking is a set of geoimages having varying resolutions corresponding to the resolutions of the inputted geoimages. Geomosaicking can be performed with the output images of the geomasking process. 
     It is additionally advantageous to project both the intersecting and unioned sections of the geospatially aligned images and/or pixels into a map domain, such as UTM or VTM. 
     It is also advantageous to overlay a geoimage with geo-features and/or geo-objects. This process is called “geooverlaying”. 
     It is further advantageous to overlay geoimages with text to identify relative and/or absolute geolocations on the image. 
     It is also advantageous to perform measurements within geoimages to obtain accurate object measurements in one-, two-, three-, and four-dimensional spaces. 
     With a newly created image, be it from georegistration or from a geomosaicking process, it is advantageous to apply a set of geospatially based grid lines disposed at predetermined geospatial units, for example, 500 meters, 1000 meters, etc. Text to indicate either relative or absolute geolocations of the image surface may be included. This process is called “geogriding”. 
     It is also advantageous to apply a set of reference lines (i.e., geogriding) using rectangular patterns, circular patterns, or lines arranged in other geometric patterns. 
     It is advantageous to index and visualize the geolocation of the boundary of each spatial component of a geomosaicked image based on the outputs of a geomasking analysis. This process is called “geoindexing”. Geoindexing has three complementary representations: (a) a multicolor geoimage, each color representing the aerial coverage of a particular geomasked image, (2) a text-based index, and (3) database file (dbf) summarizing the geospatial information of each geomasked image, a subset of the geomosaic. 
     It is also advantageous to devise a means for ordering the colorized overlaying layers to generate the color composite image of the geomosaicked image based on the outputs of a geomasking analysis. In general, the largest geomask subset is to be placed first, and the smallest geomask is the topmost color layer as shown in  FIG. 13 . 
     It is advantageous to mix geomasked and non-geomasked geoscenes to perform geoindexing in which the non-geomasked geoimages can service as a background/reference scene. 
     It is also advantageous to devise a means for coloring the mixed non-geomasked and geomasked geoscenes by using a mixture of graytone and color systems, in which a graytone geoscene can be treated as the background scene. 
     In DEM data, it is advantageous to visualize the terrain features from varying depression angle and aspect angle in the geospatial domain in which UTM is a special case of VTM. Conventional image draping that combines DEM and spectral based images is used mainly for 3-D visualizations. Consequently, image draping typically does not possess geospatial properties. Since a feature mismatch exists in cross-zone UTM-based images, DEM and terrain feature mismatches exist in conventional 3-D visualization methods with cross-UTM-zone DEM data and spectral images. Therefore, it is advantageous to perform 3-D or 4-D visualization in the VTM domain to mitigate both feature and terrain elevation mismatches. 
     A terrain contour line connects points (i.e., pixels) of equal elevation value. A contour line, therefore, can be represented by the boundary pixels of a region in a raster image of DEM data. Thus, it is advantageous to generate the geolocations of a terrain contour. It is also advantageous to depict the terrain in terms of a geocontour, a geocontour interval, as well as in a 3-D visualization geoscene. Such depiction yields a 4-D visualization system as shown in  FIG. 15 . 
     Physical objects exist on, below, and above a particular contour. Therefore, it is advantageous to visualize objects in the 3-D visualization geoscene by contour intervals, an interval being defined by two contour line values. The resulting geoscene is in reality a 4-D geoscene: x and y defines the datum plane, z 0  is the DEM dimension, and z 1  is one of the spectral/textural dimensions. 
     It is also advantageous to provide a means to generate a geo-fly-through geoscene viewed from a particular depression angle and a particular aspect angle in the geospatial domain. 
     It is also advantageous to provide a geo-fly-through geoscene that possesses terrain features in a selected terrain contour interval in the geospatial domain, in which UTM is a special case of VTM. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, there is provided a method of recognizing an object in an image. The procedure uses using multi-sensor integration through conditionally optimal geoscene generation, georegistration, geomasking, geomosaicking, geoindexing, geo-3D/4D visualization, geocontour, geocontour interval, and geo-fly-through. At least two images, one of which is typically a conditionally optimum, ortho-rectified base image, are used to generate a geoscene. The geoscene generation is performed using at least two ground control points in a latitude-longitude (“lat-long”) geospatial domain. An Affine transform may be used for coordinate transformation in the geoscene generation process. The geoscene is georegistered to produce a registered geoimage which may be output. The union and the intersection of image pixels are used to define main body and background pixels. In addition, an independently-supplied geomask can be used to define the main body non-zero-value pixels and the background, zero-value pixels. A virtual geospatial information system database may be compiled from the georegistered, geomosaicked, geomasked, geoindexed, geo-3D/4D visualization, geocontour, geocontour interval, and geo-fly-through geoimages. 
     A virtual transverse Mercator (VTM) projection is defined to help process images falling on either or both sides of the equator or across traditional UTM boundaries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawings will be provided by the Patent and Trademark Office upon request and payment of the necessary fee. 
       A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent detailed description, in which: 
         FIG. 1  is pair of satellite images of adjoining DOQQs showing spatial mismatch therebetween at a junction of two different UTM zones; 
         FIG. 2  is a key that identifies an addressing schema for DOQQs; 
         FIG. 3  is a diagram showing dual raster and vector representations of an object; 
         FIG. 4  is a vector representation of a boundary and feature attribute table; 
         FIG. 5  is an illustration of the process of representing a signal as a point object in a geoimage; 
         FIG. 6  is a 1988 USGS topoquad map of New River Inlet, N.C.; 
         FIG. 7  is a 1988 USGS DOQQ map of New River Inlet; 
         FIG. 8  is a composite scene formed by the map of  FIG. 7  and an image, for identifying a feature; 
         FIG. 9  shows a cleared area feature extracted from the composite scene of  FIG. 8 ; 
         FIG. 10  shows a runway feature extracted from the composite scene of  FIG. 8 ; 
         FIG. 11  shows a change in the runway feature of  FIG. 10  between historic data and newer data; 
         FIG. 12  shows the changes of  FIG. 11  derived from data fusion; 
         FIG. 13  is a geomasked scene with the geomasked area highlighted in red. 
         FIG. 14  is a terrain elevation image of the East portion (i.e., right-hand portion) of the image of  FIG. 1 , in which the pixel values represent terrain elevation data, rather than spectral band data. 
         FIG. 15  is a 3D/4D visualization geoimage representing a geo-fly-through scenario having one spectral based feature (vegetation) draped on top of the terrain elevation data; and 
         FIG. 16  is a flowchart showing the steps of the method of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The method of the present invention begins with generating geoscenes using four different models. A geoscene is defined in terms of an image in which every pixel is denoted by five or six locational identification systems:
         a) (x,y) coordinates in the image domain;   b) (z 0 ) coordinate for terrain elevation and/or (z 1 ) coordinate for spectral/textural data;   c) UTM or VTM coordinates in the map projection domain;   d) decimal degree in the geospatial domain; and   e) degrees, minutes and seconds in the geospatial domain.       

     Several tools exist to perform conversions between or among various coordinate systems. First, a bi-directional method for conversion between lat-long and UTM is required. Basic methods for two-way lat-long to UTM conversions are provided in Wolf and Ghilani,  Elementary Surveying: An Introduction to Geomatics  (New York: Prentice Hall, 2002). However, a superior method of performing such conversions is provided by the present invention. 
     In the UTM system, the geographic location of each zone is fixed. Consequently, the central meridian at the center of each UTM zone has a fixed location. In accordance with the present invention, however, the location of each VTM zone is movable. The width and height of a VTM zone may be the same as those of a UTM zone. In other words, by moving a 6×8 degree area, all the pixels of the images to be registered are then moved so as to be included within one particular VTM zone. This means that for all the pixels within the VTM zone, there will be only one central meridian for orientation designation. The local central meridian may be determined by the distribution of the locations of the pixels under investigation. The specification for the location meridian is as follows. 
     For a particular VTM zone to exist, all of the locations of the pixels covered by the images to be registered are geolocated. From the min and max lat-long readings of the locations of the pixels, the local central meridian is determined; from that central meridian, a particular VTM zone is generated. Thus, the specifications for the local VTM meridian are as follows: 
     a) the local meridian is the mean of all locations of the pixels under investigation; and 
     b) the local central meridian is designated by an integer (i.e., a whole, rounded number), for example 77 degrees. 
     In the UTM system, the distance designation in the longitude direction is divided into northern hemisphere and southern hemisphere, independently. Because each hemisphere starts at 0 and ends at 10 million meters, the UTM system cannot handle images having pixels dispersed over both north and south of the equator. In the VTM specification, however, both the northern hemisphere and the southern hemisphere are treated as one contiguous entity. Mathematically speaking, locations in the northern hemisphere are treated as positive numbers, while locations in the southern hemisphere as treated as negative numbers. Therefore, a third VTM specification is: 
     c) longitude readings in the northern hemisphere range from 0 to 10 million meters; and longitude readings in the southern hemisphere range from 0 to negative 10 million meters. 
     The mathematics that form the basis of the novel VTM system may be obtained from Wolf and Ghilani described hereinabove and are provided as Appendix A attached hereto. 
     To transform between two coordinate systems, the Affine transform is used. The mathematics for the Affine transform appears in Appendix B. 
     Four models for geoscene generation are used as part of the novel method of the present invention. Each model utilizes a different set of assumptions. 
     For geoscene generation, it is assumed that a conditionally optimal base image (COBI) exists, and other scenes are to be registered onto the COBI. A high resolution orthophoto with known geo-coordinates for a few pixels known as the ground control point (GCP) is an example of a COBI. 
     To generate a geoscene, an executable script that contains four sets of arguments is used:
 
Program Name−in infile_name−out outfile_name−ref “utm coordinate@x,y)−ref “utm coordinates@x,y)−ref “utm coordinate@x,y)−ref “utm coordinate@x,y)  (Eq. 1)
 
     The number of −ref controls how many ground control points are used to generate the geoscene. 
     /* −ref twice for two control points */ 
     /* −ref four times for four control points */ 
     From Equation (1), out_file is a geoscene. 
     In addition, the ground control points must have both geo-coordinate readings, and visually distinct features for manual pointing. 
     Five models for georegistration are identified. 
     Model 1: Both COBI and To-be-Matched Scenes are Orthophotos 
     Georegistration Model 1 assumes that both the base image and the to-be-registered images are ortho-rectified. In this case, only two ground control points are required. 
     Model 2: COBI is Orthophoto and To-be-Matched Images are Oblique 
     In Model 2, the requirements for the to-be-matched images are relaxed; they can be non-orthophotos. However, the number of required control points is still only two. The goal of this model is to detect the degree of the obliqueness of the to-be-matched scene. 
     Model 3: COBI is Orthophoto and To-be-Matched Images are Oblique 
     Model 3 uses three or more control points, whereas the number of control points is restricted to two for Model 2. It should be noted, however, that under the Affine transform, two, three, four or more control points may be used. The solution of the four-control-point system is generally better than a solution generated by systems using fewer control points. 
     Model 4: COBI is Still Ortho-Rectified and To-be-Matched Images are Oblique 
     In general, for Model 3, the resolution levels of the COBI and the to-be-matched images are close. For Model 4 the resolution level of to-be-matched scenes is much coarser than the resolution level of the COBI. For example, the resolution of the COBI is one meter/pixel, whereas the to-be-matched images may have a resolution of 10 meter/pixel or coarser. For each new stage of matching analysis, the user must supply a new set of control points. In Model 4, the number of control points is typically three or four and the number of matching stages is two. 
     Model 5: Both the COBI and To-be-Matched Images are Oblique 
     Model 5 is essentially an extension of Model 4 by assuming the COBI to be an oblique photo. However, among all the input images, the COBI has better geospatial control. The number of control points, however, is three or more and the number of stages for matching is two or more. 
     From the foregoing, it may be understood that when using either Model 4 or Model 5, the end product of georegistration has the same resolution. The x-scale and the y-scale of the pixel, and the orientation of the matched images are almost identical to those characteristics of the COBI. Therefore, if the COBI is an orthophoto, the matched images become near orthophoto in image quality. In other words, the inventive georegistration methodology is in reality a means to generate near-orthophoto images without having to possess the camera models of the sensors and digital elevation model (DEM) of the image coverage area. Technically, the inventive ortho-rectification approach requires that the original COBI be an orthophoto. Since this condition may not always exist, the inventive georegistration process is conditionally optimal orthophoto generation (COOG). 
     The novel COOG method of geoscene generation and georegistration of images from multiple sensors discussed above may be implemented using text-based scripts as well as interactive systems having corresponding graphic user interfaces (GUIs). Both implementations are described hereinbelow. In addition, it will be recognized that the method of the invention may be implemented in firmware using either graphical or text-based user interfaces. 
     In the GUI-based georegistration system, multiple image viewers or windows are provided. In each image viewer, basic image visualization functions (e.g., zooming, roaming, scale change, pixel intensity change/modification, scene-based gamma functions, 3-D and 4-D viewing in the geospatial domain, etc.) are provided to facilitate the selection of ground control points. One GUI-based implementation of the method of the present invention is the IMaG™ system which is used herein for purposes of disclosure. With GUI-based georegistration systems (e.g., IMaG), once the control points are manually or semi-automatically selected, geoscene generation, georegistration, geomosaicking, geomasking, and geo-3D or 4D visualization, geocontour, geocontour interval, and geo-fly-through are then automatically executed. 
     In the process of georegistration, the union of the geoimages used to create the georegistrated scenes is a geomosaic. Geomasking is process similar to georegistration, for which the geomask is an independent source. Therefore, a geomosaic is a useful by-product of the georegistration and/or geomask process. 
     An extension of a normal georegistration and a normal geomosaicking is the use of an independent geomask to define the outer limit of each inputted geoscene and, of the georegistered image cube and geomosaic. A geomask contains two kinds of pixels: non-zero-value body pixels and zero-value background pixels. It is the non-zero-value pixels that define the outer limit of each of the trimmed geoscenes. A geomask, of course, may also be a conventional gray tone image. 
     By inputting multiple geoimages into a geomasking analysis, a set of geomasked images is obtained. Each geomasked geoimage is a subset of the corresponding input geoimage to be geomasked, and its resolution is the same as that of its parent geoimage. Since the resolutions of the input scenes vary, the resolutions of the multiple geomasked scenes likewise vary. 
     Compositing the geomasked and other referenced geoimages together yield a geoindexed geoimage as shown in  FIG. 13 . A variation of the image of  FIG. 13  may be obtained using non-geomasked geoimages as the base and geooverlaying the geomasked geoscenes at the top. To differentiate between the reference geoimages and the geomasked geoscenes, graytones are used to represent the reference geoimages, and colors are used to geolocate the aerial coverage of the geomasked geoscenes. 
     By mosaicking the output scenes of a geomasking analysis, one obtains a geomosaicked image, whose spatial coverage is complemented by the individual geomasked images. 
     For visualizing multiple overlapping geomasked sub-scenes, color layers must be ordered to generate a color composite image. Otherwise, a smaller geomasked scene can become invisible because it is buried under a larger geomasked scene that totally surrounds the smaller geomasked scene. The present invention provides a method to order the multiple geomasked scenes to generate a color composite geomosaic. 
     A conventional vector database is composed of a boundary file and a corresponding feature attribute table (FAT). Three complementary data model representations are used in the geoindexing analysis of the invention: (1) raster image, (2) geoindex file, and (3) database file (dbf). The color composite scene of a geomosaic based on multiple geomasked scenes described hereinabove is a raster representation if one considers the spatial distribution of the interior pixels of each geomask subset. The color composite scene is also a vector representation (i.e., the distribution of the boundary pixels can be represented by a solid color). To complete the vector representation, a geoindex file is added to indicate the color system used to color each geomask. A database file that summarizes the geospatial characteristics of each geomasked subset within the overall geomosaicked scenes is also added. A partial listing of a geoindex file is also shown in  FIG. 13 . Thus,  FIG. 13  shows both raster and vector representations of a color composite resulting from a geomasking analysis with multiple geomasked and non-geomasked inputs. 
     An overlay may be applied to any generic geoimage, for example, an individual image, a georegistered image or a geomosaic. Such an overlay is called a “geooverlay” and the process of applying a geooverlay is called “geooverlaying”. 
     One possible geooverlay is a set of grid lines on the image, the grid lines typically corresponding to either a UTM or VTM system. This overlay is called a “geogrid”. Like any geooverlay, a geogrid may be considered a geospatial feature of the overlaid image. The process of overlaying a geogrid is called “geogridding”. It will be recognized that while geogrid implies a rectangular lattice of reference lines, other geometric patterns, for example a series of concentric circles or other geographic shapes overlaid on a geoimage may also be useful in analyzing and measuring objects and/or areas in geoimages. Consequently, the terms geogrid and geogridding apply to any such overlaid pattern. 
     A variation of the geooverlay process is to drape a spectral based feature image on top of a terrain elevation based image, generally known as digital elevation model (DEM). Typically, the DEM is viewed from particular depression angle and a particular aspect angle. The present invention departs significantly from a conventional 3-D visualization/image draping method by using VTM, rather than UTM, as the basis for generating geoimages in both spectral and DEM domains. In reality, UTM is a special case of VTM. Without using the VTM paradigm, both spectral and DEM values will be altered after image registration and consequently, feature and DEM mismatches will occur when spectral images and DEM data are distributed across multiple UTM zones and over both sides of the equator. 
     By georegistering spectral and DEM images in the geospatial domain, the present invention generates a four-dimensional (4-D) image, in which (x,y) lies on the datum plane, z 0  represents the terrain elevation, and z 1  represents one of the multiple spectral/textural bands. 
     A terrain contour line connects pixels of equal elevation value. A contour interval is a range value defined by two adjacent contour lines. A geoimage representing a particular contour interval can be generated and matched to a single or multiple spectrally-based geoimages that are georegistered to the DEM image. The results are a geocontour and a geocontour interval, respectively. By overlaying a geocontour or a geocontour interval onto a spectrally-based terrain feature, a geoimage is generated having a set of terrain features that exist within a particular DEM-based geocontour interval. 
     By draping the contour-interval based terrain features on a corresponding DEM image viewed from a particular depression and a particular aspect angle, a four dimensional geoimage is obtained in a geo-fly-through, scene visualization format is obtained. A representative geo-fly-through geoscene is shown in  FIG. 15 . 
     The method of the present invention provides a Virtual Geospacial Information System (VGIS) having a database of geospacial information contained therein. First, a spatial structure is created to identify any image generated for any region of the world. Each created spatial unit is identified by a unique, standard designation, so information about any identified region may be readily located. For example, a search engine (e.g., Google®) may easily locate information available via the Internet from anywhere in the world. 
     In the UTM system, each defined UTM zone is composed of a region of 6×8 degrees. This size is too large to define practical geospatial information items since one degree is equivalent to about 110,000 meters, and each UTM zone is therefore about 660,000 meters by 880,000 meters. This is equivalent to 660,000×880,000 pixels, assuming the resolution of the image is 1 m/pixel. 
     The resolution of currently available, commercial satellite imagery is already under 1 m/pixel. In order to conform to the existing remote sensing environment, the method of the present invention uses spatial units for a virtual geodatabase covering an area of 7.5 minutes×7.5 minutes. This, incidentally, is the same area as a topographic quadrangle produced by the United States Geological Survey (USGS). Thus, one degree has 8 quads in a linear scale. Globally, there are 2880 geo-quads, computed as follows:
 
8 quads×360=2880 quads  (Eq. 2)
 
     Unlike the UTM system, the inventive VGIS also has 2880 quads defined along the northing direction. Therefore, by using a four-digit system, the first quad can be designated as
 
0001 — 0001  (Eq. 3)
 
And the ID of the last quad is:
 
2880 — 2880.  (Eq. 4)
 
     Each geoquad may be subdivided into four quarter quads (QQ), each designated by either a numeric ID or a text ID code as follows. 
     The numeric ID code is:
 
 — 00 for the SW QQ;
 
 — 50 for the SE QQ;
 
 — 05 for the NW QQ; and
 
 — 55 for the NE QQ.  (Eq. 5)
 
     This VGIS structure (i.e., quads and quarter-quads) may be represented graphically as shown in  FIG. 3 . 
     As discussed hereinabove, the result of georegistration is a set of images all having the same resolution, the same orientation, and the same dimension. This set of images is identical to a multispectral image cube. If four or more images are available in the image cube, 20 or more additional images may be generated using linear and non-linear combinations of the at least four input images. These additional generated images are called n-transforms. 
     From a multispectral image cube containing the original images and their resultant n-transforms, an object spectral signature library may be generated. For example, if the object is a particular ground vehicle, a spectral signature of the ground vehicle may be generated by clicking on (i.e., selecting) one pixel of that particular ground vehicle. If the first image is denoted m — 1, the second image m — 2, and the n th  image is m_n. The location of a particular selected pixel located at (i,j) has a pixel value of x — 1 at (i,j)=y 1 , a pixel value of x — 2 at (i,j)=y 2 , and finally, a pixel value of x_n at (i,j)=y n , the following vector may be generated:
 
[y 1 , y 2 , . . . , y n ]  (Eq. 6)
 
     Equation (6) represents the spectral signature of the ground vehicle. A spectral signature library is composed of the spectral signatures of multiple objects. 
     An object layer is essentially a two-tone image in which one of the tone categories is an object and the other is the object&#39;s background. Usually, the object pixels are coded as white or graytone with a value of 255, and the background is back or a graytone with a value of zero. However, if the object-layer image is converted into a geoscene, then the object layer is in the geospatial domain. 
     An object layer represents an object in terms of a set of contiguous pixels. An object boundary file represents the same object in terms of a set of boundary pixels, leaving the interior as “blank” or identical to the background pixels. If the boundary file&#39;s image (x,y) is converted into corresponding geospatial coordinates, the object boundary file is in both the image domain and the geospatial domain as shown in  FIG. 3 . 
     The object layer may have multiple object regions. The IMaG system provides an object attribute table to describe the characteristics of each region. The table is called a feature attribute table (FAT), a typical FAT being shown in  FIG. 4 , generally at reference number  300 . In  FIG. 4 , columns  4  and  5 , reference numbers  302 ,  304 , respectively, are row center and column center of an extracted region. They are similar to elements of a boundary, and thus can be easily converted to corresponding geocoordinates. 
     In general, signals cannot be portrayed as an image. However, the locations where the signals are obtained can be represented as a point object in an image in both the image and geospatial domains as shown in  FIG. 4 . 
     With the IMaG system, a user processes data and information using words and concepts. Thus, the user can generate new objects by fusing existing objects according to their spatial relationships. Object change detection (i.e., the change in a identified object over time) is such an example as illustrated in  FIGS. 6-12 . 
     All of the objects in the VGIS cell discussed above can be represented for both information processing and visualization purposes. For data processing, the object layer is represented by 8-bit pixels, whereas for visualization, the object is represented by a solid color or translucent color overlaid on a background scene, which can be either graytone images or color images. 
     With the global or virtual geoquad structure of the present invention as shown in  FIG. 2 , all of the objects become the elements of a virtual geoquad-based object library. By using the geoquad ID as a subset of an object name, such as 0001 — 0001 as the prefix, all of the posted objects within that geoquad are readily available to the user(s). For example, if the specific objects in a geoquad are posted with four feature layers (e.g., water, vegetation, roads, and buildings), the object file names might be: 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 File Names in Geoquad 0001_0001 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   
                 0001_0001_water.pgm 
               
               
                   
                   
                 0001_0001_vegetation.pgm 
               
               
                   
                   
                 0001_0001_roads.pgm 
               
               
                   
                   
                 0001_0001_buildings.pgm 
               
               
                   
                   
               
             
          
         
       
     
     Referring now to  FIG. 16 , there is shown a flow chart of the method of the present invention, generally at reference number  310 . One or more multisensor input images  312 , along with a reference multisensor image, typically from VGIS database  316 , are used to generate a geoscene, step  318 . 
     Typically, a multisensor input image  314  serves as the base image and is an ortho or near-ortho image that has a higher resolution than do the image(s) represented by multisensor images  312 . Thus, the base reference image  314  is referred to as a conditionally optimal base image (COBI) and is applied to step  318 . Multisensor images  312  are registered to the COBI  314  on two or more ground control points (GCP). The GCPs in COBI  314  are assumed to have accurate lat-long readings (i.e., geocoordinates). 
     Georegistration in the lat-long domain is next performed, step  320 . If the resolution of the to-be-registered image is very low, multiple stages of georegistration may be required. 
     The registered geoscenes are output as an image cube, step  322 . The characteristics of the registered geoscenes are provided in a header. Information contained in the header includes such information as: resolution in both x-axis and y-axis, orientation along which longitude (central meridian), north offset, whether UTM or VTM was used, etc. This image cube is in and of itself a useful end product of the inventive method. The registered geoscense are stored in database  316  as well as made available for additional processing. 
     The registered geoscenes generated in step  322  may be converted to conditional optional orthoimages, step  324 . However, in order to do this, image  314  (i.e., the COBI) must be an orthoimage. These orthoimages and their n-transforms constitute yet another useful output product of the inventive method. 
     Both raster and vector images may be generated from the orthoimages, step  326 . These dual raster/vector images also may be stored in the VGIS database  316 . 
     The orthoimages generated in step  324  may be further processed to derive spectral signatures therefrom, step  328 . These spectral signatures form at least a portion of a spectral signature library. As with several aforementioned outputs of the inventive process, both individual spectral signatures as well as a spectral signature library are also useful outputs. These outputs also may be stored in VGIS database  316 . 
     Spectral signature based objects may be formed, step  330 , from observed, georegistered scenes  332 , plus their n-transforms and used as elements for matching against a spectral signature library. 
     With the input of optimal independent sources (including terrain elevations)  334 , the inventive system becomes even more open and adaptive. The terrain elevation images may be combined with spectral signature based objects, step  330 , to generate feature draped terrain scenes, step  336 . 
     Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to examples chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. 
     Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.