Method and apparatus for capturing, geolocating and measuring oblique images

A computerized system for displaying, geolocating, and taking measurements from captured oblique images includes a data file accessible by the computer system. The data file includes a plurality of image files corresponding to a plurality of captured oblique images, and positional data corresponding to the images. Image display and analysis software is executed by the system for reading the data file and displaying at least a portion of the captured oblique images. The software retrieves the positional data for one or more user-selected points on the displayed image, and calculates a separation distance between any two or more selected points. The separation distance calculation is user-selectable to determine various parameters including linear distance between, area encompassed within, relative elevation of, and height difference between selected points.

TECHNICAL FIELD

The present invention relates to photogrammetry. More particularly, the present invention relates to a method and apparatus for capturing oblique images and for measuring the objects and distances between the objects depicted therein.

BACKGROUND

Photogrammetry is the science of making measurements of and between objects depicted within photographs, especially aerial photographs. Generally, photogrammetry involves taking images of terrestrial features and deriving data therefrom, such as, for example, data indicating relative distances between and sizes of objects within the images. Photogrammetry may also involve coupling the photographs with other data, such as data representative of latitude and longitude. In effect, the image is overlaid and conformed to a particular spatial coordinate system.

Conventional photogrammetry involves the capture and/or acquisition of orthogonal images. The image-capturing device, such as a camera or sensor, is carried by a vehicle or platform, such as an airplane or satellite, and is aimed at a nadir point that is directly below and/or vertically downward from that platform. The point or pixel in the image that corresponds to the nadir point is the only point/pixel that is truly orthogonal to the image-capturing device. All other points or pixels in the image are actually oblique relative to the image-capturing device. As the points or pixels become increasingly distant from the nadir point they become increasingly oblique relative to the image-capturing device and the ground sample distance (i.e., the surface area corresponding to or covered by each pixel) also increases. Such obliqueness in an orthogonal image causes features in the image to be distorted, especially images relatively distant from the nadir point.

Such distortion is removed, or compensated for, by the process of ortho-rectification which, in essence, removes the obliqueness from the orthogonal image by fitting or warping each pixel of an orthogonal image onto an orthometric grid or coordinate system. The process of ortho-rectification creates an image wherein all pixels have the same ground sample distance and are oriented to the north. Thus, any point on an ortho-rectified image can be located using an X, Y coordinate system and, so long as the image scale is known, the length and width of terrestrial features as well as the relative distance between those features can be calculated.

Although the process of ortho-rectification compensates to a degree for oblique distortions in an orthogonal image, it introduces other undesirable distortions and/or inaccuracies in the ortho-rectified orthogonal image. Objects depicted in ortho-rectified orthogonal images may be difficult to recognize and/or identify since most observers are not accustomed to viewing objects, particularly terrestrial features, from above. To an untrained observer an ortho-rectified image has a number of distortions. Roads that are actually straight appear curved and buildings may appear to tilt. Further, ortho-rectified images contain substantially no information as to the height of terrestrial features. The interpretation and analysis of orthogonal and/or ortho-rectified orthogonal images is typically performed by highly-trained analysts whom have undergone years of specialized training and experience in order to identify objects and terrestrial features in such images.

Thus, although orthogonal and ortho-rectified images are useful in photogrammetry, they lack information as to the height of features depicted therein and require highly-trained analysts to interpret detail from what the images depict.

Oblique images are images that are captured with the image-capturing device aimed or pointed generally to the side of and downward from the platform that carries the image-capturing device. Oblique images, unlike orthogonal images, display the sides of terrestrial features, such as houses, buildings and/or mountains, as well as the tops thereof. Thus, viewing an oblique image is more natural and intuitive than viewing an orthogonal or ortho-rectified image, and even casual observers are able to recognize and interpret terrestrial features and other objects depicted in oblique images. Each pixel in the foreground of an oblique image corresponds to a relatively small area of the surface or object depicted (i.e., each foreground pixel has a relatively small ground sample distance) whereas each pixel in the background corresponds to a relatively large area of the surface or object depicted (i.e., each background pixel has a relatively large ground sample distance). Oblique images capture a generally trapezoidal area or view of the subject surface or object, with the foreground of the trapezoid having a substantially smaller ground sample distance (i.e., a higher resolution) than the background of the trapezoid.

Oblique images are considered to be of little or no use in photogrammetry. The conventional approach of forcing the variously-sized foreground and background pixels of an oblique image into a uniform size to thereby warp the image onto a coordinate system dramatically distorts the oblique image and thereby renders identification of objects and the taking of measurements of objects depicted therein a laborious and inaccurate task. Correcting for terrain displacement within an oblique image by using an elevation model further distorts the images thereby increasing the difficulty with which measurements can be made and reducing the accuracy of any such measurements.

Thus, although oblique images are considered as being of little or no use in photogrammetry, they are easily interpreted and contain information as to the height of features depicted therein.

Therefore, what is needed in the art is a method and apparatus for photogrammetry that enable geo-location and accurate measurements within oblique images.

Moreover, what is needed in the art is a method and apparatus for photogrammetry that enable the measurement of heights and relative heights of objects within an image.

Furthermore, what is needed in the art is a method and apparatus for photogrammetry that utilizes more intuitive and natural images.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for capturing, displaying, and making measurements of objects and distances between objects depicted within oblique images.

The present invention comprises, in one form thereof, a computerized system for displaying, geolocating, and taking measurements from captured oblique images. The system includes a data file accessible by the computer system. The data file includes a plurality of image files corresponding to a plurality of captured oblique images, and positional data corresponding to the images. Image display and analysis software is executed by the system for reading the data file and displaying at least a portion of the captured oblique images. The software retrieves the positional data for one or more user-selected points on the displayed image, and calculates a separation distance between any two or more selected points. The separation distance calculation is user-selectable to determine various parameters including linear distance between, area encompassed within, relative elevation of, and height difference between selected points.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and particularly toFIG. 1, one embodiment of an apparatus for capturing and geolocating oblique images of the present invention is shown. Apparatus10includes a platform or vehicle20that carries image-capturing and geolocating system30.

Platform20, such as, for example, an airplane, space shuttle, rocket, satellite, or any other suitable vehicle, carries image-capturing system30over a predefined area of and at one or more predetermined altitudes above surface31, such as, for example, the earth's surface or any other surface of interest. As such, platform20is capable of controlled movement or flight, either manned or unmanned, along a predefined flight path or course through, for example, the earth's atmosphere or outer space. Image-capturing platform20includes a system for generating and regulating power (not shown) that includes, for example, one or more generators, fuel cells, solar panels, and/or batteries, for powering image-capturing system30.

Image-capturing and geo-locating system30, as best shown inFIG. 2, includes image capturing devices32aand32b, a global positioning system (GPS) receiver34, an inertial navigation unit (INU)36, clock38, gyroscope40, compass42and altimeter44, each of which are interconnected with image-capturing computer system46.

Image-capturing devices32aand32b, such as, for example, conventional cameras, digital cameras, digital sensors, charge-coupled devices, or other suitable image-capturing devices, are capable of capturing images photographically or electronically. Image-capturing devices32aand32bhave known or determinable characteristics including focal length, sensor size and aspect ratio, radial and other distortion terms, principal point offset, pixel pitch, and alignment. Image-capturing devices32aand32bacquire images and issue image data signals (IDS)48aand48b, respectively, corresponding to the particular images or photographs taken and which are stored in image-capturing computer system46, as will be more particularly described hereinafter.

As best shown inFIG. 1, image-capturing devices32aand32bhave respective central axes A1and A2, and are mounted to platform20such that axes A1and A2are each at an angle of declination θ relative to a horizontal plane P. Declination angle θ is virtually any oblique angle, but is preferably from approximately 20° (twenty degrees) to approximately 60° (sixty degrees) and is most preferably from approximately 40° (forty degrees) to approximately 50° (fifty degrees).

GPS receiver34receives global positioning system signals52that are transmitted by one or more global positioning system satellites54. The GPS signals52, in known fashion, enable the precise location of platform20relative to surface31to be determined. GPS receiver34decodes GPS signals52and issues location signals/data56, that are dependent at least in part upon GPS signals52and which are indicative of the precise location of platform20relative to surface31. Location signals/data56corresponding to each image captured by image-capturing devices32aand32bare received and stored by image-capturing computer system46.

INU36is a conventional inertial navigation unit that is coupled to and detects changes in the velocity, including translational and rotational velocity, of image-capturing devices32aand32band/or platform20. INU36issues velocity signals/data58indicative of such velocities and/or changes therein to image-capturing computer system46, which stores velocity signals/data58corresponding to each image captured by image-capturing devices32aand32bare received and stored by image-capturing computer system46.

Clock38keeps a precise time measurement (time of validity) that is used to synchronize events within image-capturing and geo-locating system30. Clock38provides time data/clock signal62that is indicative of the precise time that an image is taken by image-capturing devices32aand32b. Time data62is also provided to and stored by image-capturing computer system46. Alternatively, clock38is integral with image-capturing computer system46, such as, for example, a clock software program.

Gyroscope40is a conventional gyroscope as commonly found on airplanes and/or within commercial navigation systems for airplanes. Gyroscope40provides signals including pitch signal64, roll signal66and yaw signal68, which are respectively indicative of pitch, roll and yaw of platform20. Pitch signal64, roll signal66and yaw signal68corresponding to each image captured by image-capturing devices32aand32bare received and stored by image-capturing computer system46.

Compass42, such as, for example, a conventional electronic compass, indicates the heading of platform20. Compass42issues heading signal/data72that is indicative of the heading of platform20. Image-capturing computer system46receives and stores the heading signals/data72that correspond to each image captured by image-capturing devices32aand32b.

Altimeter44indicates the altitude of platform20. Altimeter44issues altitude signal/data74, and image-capturing computer system46receives and stores the altitude signal/data74that correspond to each image captured by image-capturing devices32aand32b.

As best shown inFIG. 3, image-capturing computer system46, such as, for example, a conventional laptop personal computer, includes memory82, input devices84aand84b, display device86, and input and output (I/O) ports88. Image-capturing computer system46executes image and data acquiring software90, which is stored in memory82. Memory82also stores data used and/or calculated by image-capturing computer system46during the operation thereof, and includes, for example, non-volatile read-only memory, random access memory, hard disk memory, removable memory cards and/or other suitable memory storage devices and/or media. Input devices84aand84b, such as, for example, a mouse, keyboard, joystick, or other such input devices, enable the input of data and interaction of a user with software being executed by image-capturing computer system46. Display device86, such as, for example, a liquid crystal display or cathode ray tube, displays information to the user of image-capturing computer system46. I/O ports88, such as, for example, serial and parallel data input and output ports, enable the input and/or output of data to and from image-capturing computer system46.

Each of the above-described data signals is connected to image-capturing computer system46. More particularly, image data signals48, location signals56, velocity signals58, time data signal62, pitch, roll and yaw signals64,66and68, respectively, heading signal72and altitude signal74are received via I/O ports88by and stored within memory82of image-capturing computer system46.

In use, image-capturing computer system46executes image and data acquiring software90, which, in general, controls the reading, manipulation, and storing of the above-described data signals. More particularly, image and data acquiring software90reads image data signals48aand48band stores them within memory82. Each of the location signals56, velocity signals58, time data signal62, pitch, roll and yaw signals64,66and68, respectively, heading signal72and altitude signal74that represent the conditions existing at the instant an image is acquired or captured by image-capturing devices32aand32band which correspond to the particular image data signals48aand48brepresenting the captured images are received by image-capturing computer system46via I/O ports88. Image-capturing computer system46executing image and data acquiring software90issues image-capture signal92to image-capturing devices32aand32bto thereby cause those devices to acquire or capture an image at predetermined locations and/or at predetermined intervals which are dependent at least in part upon the velocity of platform20.

Image and data acquiring software90decodes as necessary and stores the aforementioned signals within memory82, and associates the data signals with the corresponding image signals48aand48b. Thus, the altitude, orientation in terms of roll, pitch, and yaw, and the location of image-capturing devices32aand32brelative to surface31, i.e., longitude and latitude, for every image captured by image-capturing devices32aand32bis known.

Platform20is piloted or otherwise guided through an image-capturing path that passes over a particular area of surface31, such as, for example, a predefined area of the surface of the earth or of another planet. Preferably, the image-capturing path of platform20is at right angles to at least one of the boundaries of the area of interest. The number of times platform20and/or image-capturing devices32a,32bpass over the area of interest is dependent at least in part upon the size of the area and the amount of detail desired in the captured images. The particular details of the image-capturing path of platform20are described more particularly hereinafter.

As platform20passes over the area of interest a number of oblique images are captured by image-capturing devices32aand32b. As will be understood by those of ordinary skill in the art, images are captured or acquired by image-capturing devices32aand32bat predetermined image capture intervals which are dependent at least in part upon the velocity of platform20.

Image data signals48aand48bcorresponding to each image acquired are received by and stored within memory82of image-capturing computer system46via I/O ports88. Similarly, the data signals (i.e., image data signals48, location signals56, velocity signals58, time data signal62, pitch, roll and yaw signals64,66and68, respectively, heading signal72and altitude signal74) corresponding to each captured image are received and stored within memory82of image-capturing computer system46via I/O ports88. Thus, the location of image-capturing device32aand32brelative to surface32at the precise moment each image is captured is recorded within memory82and associated with the corresponding captured image.

As best shown inFIG. 1, the location of image-capturing devices32aand32brelative to the earth corresponds to the nadir point N of orthogonal image102. Thus, the exact geo-location of the nadir point N of orthogonal image102is indicated by location signals56, velocity signals58, time data signal62, pitch, roll and yaw signals64,66and68, respectively, heading signal72and altitude signal74. Once the nadir point N of orthogonal image102is known, the geo-location of any other pixel or point within image102is determinable in known manner.

When image-capturing devices32aand32bare capturing oblique images, such as oblique images104aand104b(FIG. 1), the location of image-capturing devices32aand32brelative to surface31is similarly indicated by location signals56, velocity signals58, time data signal62, pitch, roll and yaw signals64,66and68, respectively, heading signal72, altitude signal74and the known angle of declination θ of the primary axes A1and A2of image-capturing devices32aand32b, respectively.

It should be particularly noted that a calibration process enables image and data acquiring software90to incorporate correction factors and/or correct for any error inherent in or due to image-capturing device32, such as, for example, error due to calibrated focal length, sensor size, radial distortion, principal point offset, and alignment.

Image and data acquiring software90creates and stores in memory82one or more output image and data files120. More particularly, image and data acquiring software90converts image data signals48a,48band the orientation data signals (i.e., image data signals48, location signals56, velocity signals58, time data signal62, pitch, roll and yaw signals64,66and68, respectively, heading signal72and altitude signal74) into computer-readable output image and data files120. As best shown inFIG. 4, output image and data file120contains a plurality of captured image files I1, I2, . . . , Incorresponding to captured oblique images, and the positional data CPD1, CPD2, . . . , CPDncorresponding thereto.

Image files I1, I2, . . . , Inof the image and data file120are stored in virtually any computer-readable image or graphics file format, such as, for example, JPEG, TIFF, GIF, BMP, or PDF file formats, and are cross-referenced with the positional data CPD1, CPD2, . . . , CPDnwhich is also stored as computer-readable data. Alternatively, positional data CPD1, CPD2, . . . , CPDnis embedded within the corresponding image files I1, I2, . . . , Inin known manner. Image data files120are then processed, either by image and data acquiring software90or by post-processing, to correct for errors, such as, for example, errors due to flight path deviations and other errors known to one of ordinary skill in the art. Thereafter, image data files120are ready for use to display and make measurements of and between the objects depicted within the captured images, including measurements of the heights of such objects.

Referring now toFIG. 5, image display and measurement computer system130, such as, for example, a conventional desktop personal computer or a mobile computer terminal in a police car, includes memory132, input devices134aand134b, display device136, and network connection138. Image-capturing computer system130executes image display and analysis software140, which is stored in memory132. Memory132includes, for example, non-volatile read-only memory, random access memory, hard disk memory, removable memory cards and/or other suitable memory storage devices and/or media. Input devices134aand134b, such as, for example, a mouse, keyboard, joystick, or other such input devices, enable the input of data and interaction of a user with image display and analysis software140being executed by image display and measurement computer system130. Display device136, such as, for example, a liquid crystal display or cathode ray tube, displays information to the user of image display and measurement computer system130. Network connection138connects image display and measurement computer system130to a network (not shown), such as, for example, a local-area network, wide-area network, the Internet and/or the World Wide Web.

In use, and referring now toFIG. 6, image display and measurement computer system130executing image display and analysis software140accesses one or more output image and data files120that have been read into memory132, such as, for example, via network connection138, a floppy disk drive, removable memory card or other suitable means. One or more of the captured images I1, I2, . . . , Inof output image and data files120is thereafter displayed as displayed oblique image142under the control of image display and analysis software140. At approximately the same time, one or more data portions CPD1, CPD2, . . . , CPDncorresponding to displayed oblique image142are read into a readily-accessible portion of memory132.

It should be particularly noted that displayed oblique image142is displayed substantially as captured, i.e., displayed image142is not warped or fitted to any coordinate system nor is displayed image142ortho-rectified. Rather than warping displayed image142to a coordinate system in order to enable measurement of objects depicted therein, image display and analysis software140, in general, determines the geo-locations of selected pixels only as needed, or “on the fly”, by referencing data portions CPD1, CPD2, . . . , CPDnof output image and data files120and calculating the position and/or geo-location of those selected pixels using one or more projection equations as is more particularly described hereinafter.

Generally, a user of display and measurement computer system130takes measurements of and between objects depicted in displayed oblique image142by selecting one of several available measuring modes provided within image display and analysis software140. The user selects the desired measurement mode by accessing, for example, a series of pull-down menus or toolbars M, or via keyboard commands. The measuring modes provided by image display and analysis software140include, for example, a distance mode that enables measurement of the distance between two or more selected points, an area mode that enables measurement of the area encompassed by several selected and interconnected points, a height mode that enables measurement of the height between two or more selected points, and an elevation mode that enables the measurement of the change in elevation of one selected point relative to one or more other selected points.

After selecting the desired measurement mode, the user of image display and analysis software140selects with one of input devices134a,134ba starting point or starting pixel152and an ending point or pixel154on displayed image142, and image display and analysis software140automatically calculates and displays the quantity sought, such as, for example, the distance between starting pixel152and ending pixel154.

When the user selects starting point/pixel152, the geo-location of the point corresponding thereto on surface31is calculated by image display and analysis software140which executes one or more projection equations using the data portions CPD1, CPD2, . . . , CPDnof output image and data files120that correspond to the particular image being displayed. The longitude and latitude of the point on surface31corresponding to pixel152are then displayed by image display and analysis software140on display136, such as, for example, by superimposing the longitude and latitude on displayed image142adjacent the selected point/pixel or in pop-up display box elsewhere on display136. The same process is repeated by the user for the selection of the end pixel/point154, and by image display and analysis software140for the retrieval and display of the longitude and latitude information.

The calculation of the distance between starting and ending points/pixels152,154, respectively, is accomplished by determining the geo-location of each selected pixel152,154“on the fly”. The data portions CPD1, CPD2, . . . , CPDnof output image and data file120corresponding to the displayed image are retrieved, and the geo-location of the point on surface31corresponding to each selected pixel are then determined. The difference between the geo-locations corresponding to the selected pixels determines the distance between the pixels.

As an example of how the geo-location of a given point or pixel within displayed oblique image142is determined, we will assume that displayed image142corresponds to orthogonal image104a(FIG. 1). The user of image display and analysis software140selects pixel154which, for simplicity, corresponds to center C (FIG. 1) of oblique image104a. As shown inFIG. 1, line106extends along horizontal plane G from a point108thereon that is directly below image-capturing device32ato the center C of the near border or edge108of oblique image104a. An extension of primary axis A1intersects with center C. Angle Ø is the angle formed between line106the extension of primary axis A1. Thus, a triangle (not referenced) is formed having vertices at image-capturing device32a, point108and center C, and having sides106, the extension of primary axis A1and vertical (dashed) line110between point108and image-capturing device32a.

Ground plane G is a substantially horizontal, flat or non-sloping ground plane (and which typically will have an elevation that reflects the average elevation of the terrain), and therefore the above-described triangle includes a right angle between side/line110and side/line106. Since angle Ø and the altitude of image-capturing device32(i.e., the length of side110) are known, the hypotenuse (i.e., the length of the extension of primary axis A1) and remaining other side of the right triangle are calculated by simple geometry. Further, since the exact position of image-capturing device32ais known at the time the image corresponding to displayed image142was captured, the latitude and longitude of point108are also known. Knowing the length of side106, calculated as described above, enables the exact geo-location of pixel154corresponding to center C of oblique image104ato be determined by image display and analysis software140. Once the geo-location of the point corresponding to pixel154is known, the geo-location of any other pixel in displayed oblique image142is determinable using the known camera characteristics, such as, for example, focal length, sensor size and aspect ratio, radial and other distortion terms, etc.

The distance between the two or more points corresponding to two or more selected pixels within displayed image142is calculated by image display and analysis software140by determining the difference between the geo-locations of the selected pixels using known algorithms, such as, for example, the Gauss formula and/or the vanishing point formula, dependent upon the selected measuring mode. The measurement of objects depicted or appearing in displayed image142is conducted by a substantially similar procedure to the procedure described above for measuring distances between selected pixels. For example, the lengths, widths and heights of objects, such as, for example, buildings, rivers, roads, and virtually any other geographic or man-made structure, appearing within displayed image142are measured by selecting the appropriate/desired measurement mode and selecting starting and ending pixels.

It should be particularly noted that in the distance measuring mode of image display and analysis software140the distance between the starting and ending points/pixels152,154, respectively, is determinable along virtually any path, such as, for example, a “straight-line” path P1or a path P2that involves the selection of intermediate points/pixels and one or more “straight-line” segments interconnected therewith.

It should also be particularly noted that the distance measuring mode of image display and analysis software140determines the distance between selected pixels according to a “walk the earth” method. The “walk the earth method” creates a series of interconnected line segments, represented collectively by paths P1and P2, that extend between the selected pixels/points and which lie upon or conform to the planar faces of a series of interconnected facets that define a tessellated ground plane. The tessellated ground plane, as will be more particularly described hereinafter, closely follows or recreates the terrain of surface31, and therefore paths P1and P2also closely follow the terrain of surface31. By measuring the distance along the terrain simulated by the tessellated ground plane, the “walk the earth” method provides for a more accurate and useful measurement of the distance between selected points than the conventional approach, which warps the image onto a flat earth or average elevation plane system and measures the distance between selected points along the flat earth or plane and substantially ignores variations in terrain between the points.

For example, a contractor preparing to bid on a contract for paving a roadway over uneven or hilly terrain can determine the approximate amount or area of roadway involved using image display and analysis software140and the “walk the earth” measurement method provided thereby. The contractor can obtain the approximate amount or area of roadway from his or her own office without having to send a surveying crew to the site to obtain the measurements necessary.

In contrast to the “walk the earth” method provided by the present invention, the “flat earth” or average elevation distance calculating approaches include inherent inaccuracies when measuring distances between points and/or objects disposed on uneven terrain and when measuring the sizes and/or heights of objects similarly disposed. Even a modest slope or grade in the surface being captured results in a difference in the elevation of the nadir point relative to virtually any other point of interest thereon. Thus, referring again toFIG. 1, the triangle formed by line106, the extension of primary axis A1and the vertical (dashed) line110between point108and image-capturing device32amay not be a right triangle. If such is the case, any geometric calculations assuming that triangle to be a right triangle would contain errors, and such calculations would be reduced to approximations due to even a relatively slight gradient or slope between the points of interest.

For example, if surface31slopes upward between nadir point N and center C at the near or bottom edge108of oblique image104then second line110intersects surface31before the point at which such intersection would occur on a level or non-sloping surface31. If center C is fifteen feet higher than nadir point N and with a declination angle θ equal to 40° (forty degrees), the calculated location of center C would be off by approximately 17.8 feet without correction for the change in elevation between the points.

As generally discussed above, in order to compensate at least in part for changes in elevation and the resultant inaccuracies in the measurement of and between objects within image142, image display and analysis software140references, as necessary, points within displayed image142and on surface31to a pre-calculated tessellated or faceted ground plane generally designated160inFIG. 6. Tessellated ground plane160includes a plurality of individual facets162a,162b,162c, etc., each of which are interconnected to each other and are defined by four vertices (not referenced, but shown as points) having respective elevations. Adjacent pairs of facets162a,162b,162c, etc., share two vertices. Each facet162a,162b,162c, etc., has a respective pitch and slope. Tessellated ground plane160is created based upon various data and resources, such as, for example, topographical maps, and/or digital raster graphics, survey data, and various other sources.

Generally, the geo-location of a point of interest on displayed image142is calculated by determining which of facets162a,162b,162c, etc., correspond to that point of interest. Thus, the location of the point of interest is calculated based on the characteristics, i.e., elevation, pitch and slope, of facets162a,162b,162c, etc., rather than based upon a flat or average-elevation ground plane. Error is introduced only in so far as the topography of surface31and the location of the point of interest thereon deviate from the planar surface of the facet162a,162b,162c, etc, within which the point of interest lies. That error is reducible through a bilinear interpolation of the elevation of the point of interest within a particular one of facets162a,162b,162c, etc., and using that interpolated elevation in the location calculation performed by image display and analysis software140.

To use tessellated ground plane160, image display and analysis software140employs a modified ray-tracing algorithm to find the intersection of the ray projected from the image-capturing device32aor32btowards surface31and tessellated ground plane160. The algorithm determines not only which of facets162a,162b,162c, etc., is intersected by the ray, but also where within the facet the intersection occurs. By use of bi-linear interpolation, a fairly precise ground location can be determined. For the reverse projection, tessellated ground plane160is used to find the ground elevation value for the input ground location also using bi-linear interpolation. The elevation and location are then used to project backwards through a model of the image-capturing device32aor32bto determine which of the pixels within displayed image142corresponds to the given location.

More particularly, and as an example, image display and analysis software140performs and/or calculates the geo-location of point164by superimposing and/or fitting tessellated ground plane160to at least a portion166, such as, for example, a hill, of surface31. It should be noted that only a small portion of tessellated ground plane160and facets162a,162b,162c, etc., thereof is shown along the profile of portion166of surface31. As discussed above, each of facets162a,162b,162c,etc., are defined by four vertices, each of which have respective elevations, and each of the facets have respective pitches and slopes. The specific position of point164upon the plane/surface of the facet162a,162b,162c, etc., within which point164(or its projection) lies is determined as described above.

Tessellated ground plane160is preferably created outside the operation of image display and measurement computer system130and image display and analysis software140. Rather, tessellated ground plane160takes the form of a relatively simple data table or look-up table168stored within memory132of and/or accessible to image display and measurement computer system130. The computing resources required to calculate the locations of all the vertices of the many facets of a typical ground plane do not necessarily have to reside within image display and measurement computer system130. Thus, image display and measurement computer system130is compatible for use with and executable by a conventional personal computer without requiring additional computing resources.

Calculating tessellated ground plane160outside of image display and measurement computer system130enables virtually any level of detail to be incorporated into tessellated ground plane160, i.e., the size and/or area covered by or corresponding to each of facets162a,162b,162c, etc., can be as large or as small as desired, without significantly increasing the calculation time, slowing the operation of, nor significantly increasing the resources required by image display and measurement computer system130and/or image display and analysis software140. Display and measurement computer system130can therefore be a relatively basic and uncomplicated computer system.

The size of facets162a,162b,162c, etc., are uniform in size throughout a particular displayed image142. For example, if displayed image142corresponds to an area that is approximately 750 feet wide in the foreground by approximately 900 feet deep, the image can be broken into facets that are approximately 50 square feet, thus yielding about 15 facets in width and 18 facets in depth. Alternatively, the size of facets162a,162b,162c, etc., are uniform in terms of the number of pixels contained therein, i.e., each facet is the same number of pixels wide and the same number of pixels deep. Facets in the foreground of displayed image142, where the pixel density is greatest, would therefore be dimensionally smaller than facets in the background of displayed image142where pixel density is lowest. Since it is desirable to take most measurements in the foreground of a displayed image where pixel density is greatest, creating facets that are uniform in terms of the number of pixels they contain has the advantage of providing more accurate measurements in the foreground of displayed image142relative to facets that are dimensionally uniform.

Another advantage of using pixels as a basis for defining the dimensions of facets162a,162b,162c, etc., is that the location calculation (pixel location to ground location) is relatively simple. A user operates image display and measurement computer system130to select a pixel within a given facet, image display and analysis software140looks up the data for the facet corresponding to the selected pixel, the elevation of the selected pixel is calculated as discussed above, and that elevation is used within the location calculation.

Generally, the method of capturing oblique images of the present invention divides an area of interest, such as, for example, a county, into sectors of generally uniform size, such as, for example, sectors that are approximately one square mile in area. This is done to facilitate the creation of a flight plan to capture oblique images covering every inch of the area of interest, and to organize and name the sectors and/or images thereof for easy reference, storage and retrieval (a process known in the art as “sectorization”). Because the edges of any geographic area of interest, such as a county, rarely falls on even square mile boundaries, the method of capturing oblique images of the present invention provides more sectors than there are square miles in the area of interest—how many more depends largely on the length of the county borders as well as how straight or jagged they are. Typically, you can expect one extra sector for every two to three miles of border. So if a county or other area of interest is roughly 20 miles by 35 miles, or 700 square miles, the area will be divided into approximately from 740 to 780 sectors.

The method of capturing oblique images of the present invention, in general, captures the oblique images from at least two compass directions, and provides full coverage of the area of interest from at least those two compass directions. Referring now toFIGS. 7 and 8, a first embodiment of a method for capturing oblique images of the present invention is shown. For sake of clarity,FIG. 7 and 8is based on a system having only one image-capturing device. However, it is to be understood that two or more image-capturing devices can be used.

The image-capturing device captures one or more oblique images during each pass over area200. The image-capturing device, as discussed above, is aimed at an angle over area200to capture oblique images thereof. Area200is traversed in a back-and-forth pattern, similar to the way a lawn is mowed, by the image-carrying device and/or the platform to ensure double coverage of area200.

More particularly, area200is traversed by image-carrying device32and/or platform20following a first path202to thereby capture oblique images of portions202a,202b, and202cof area200. Area200is then traversed by image-carrying device32and/or platform20following a second path204that is parallel and spaced apart from, and in an opposite direction to, i.e., 180° (one-hundred and eighty degrees) from, first path202, to thereby capture oblique images of portions204a,204b,204cof area200. By comparingFIGS. 7 and 8, it is seen that a portion207(FIG. 8) of area200is covered by images202a-ccaptured from a first direction or perspective, and by images204a-ccaptured from a second direction or perspective. As such, the middle portion of area200is 100% (one-hundred percent) double covered. The above-described pattern of traversing or passing over area200along opposing paths that are parallel to paths202and204is repeated until the entirety of area200is completely covered by at least one oblique image captured from paths that are parallel to, spaced apart from each other as dictated by the size of area200, and in the same direction as paths202and204to thereby one-hundred percent double cover area200from those perspectives/directions.

If desired, and for enhanced detail, area200is covered by two additional opposing and parallel third and fourth paths206and208, respectively, that are perpendicular to paths202and204as shown inFIGS. 9 and 10. Area200is therefore traversed by image-carrying device32and/or platform20following third path206to capture oblique images of portions206a,206band206cof area200, and is then traversed along fourth path208that is parallel, spaced apart from, and opposite to third path206to capture oblique images of portions208a,208band208cof area200. This pattern of traversing or passing over area200along opposing paths that are parallel to paths206and208is similarly repeated until the entirety of area200is completely covered by at least one oblique image captured from paths that are parallel to, spaced apart from as dictated by the size of area200, and in the same direction as paths206and208to thereby one-hundred percent double cover area200from those directions/perspectives.

As described above, image-carrying device32and/or platform20, traverses or passes over area200along a predetermined path. However, it is to be understood that image-carrying device and/or platform20do not necessarily pass or traverse directly over area200but rather may pass or traverse an area adjacent, proximate to, or even somewhat removed from, area200in order to ensure that the portion of area200that is being imaged falls within the image-capture field of the image-capturing device. Path202, as shown inFIG. 7, is such a path that does not pass directly over area200but yet captures oblique images thereof.

The present invention is capable of capturing images at various levels of resolution or ground sample distances. A first level of detail, hereinafter referred to as a community level, has a ground sample distance of, for example, approximately two-feet per pixel. For orthogonal community-level images, the ground sample distance remains substantially constant throughout the image. Orthogonal community-level images are captured with sufficient overlap to provide stereo pair coverage. For oblique community-level images, the ground sample distance varies from, for example, approximately one-foot per pixel in the foreground of the image to approximately two-feet per pixel in the mid-ground of the image, and to approximately four-feet per pixel in the background of the image. Oblique community-level images are captured with sufficient overlap such that each area of interest is typically covered by at least two oblique images from each compass direction captured. Approximately ten oblique community-level images are captured per sector.

A second level of detail, hereinafter referred to as a neighborhood level, is significantly more detailed than the community-level images. Neighborhood-level images have a ground sample distance of, for example, approximately six-inches per pixel. For orthogonal neighborhood-level images, the ground sample distance remains substantially constant. Oblique neighborhood-level images have a ground sample distance of, for example, from approximately four-inches per pixel in the foreground of the image to approximately six-inches per pixel in the mid-ground of the image, and to approximately ten-inches per pixel in the background of the image. Oblique neighborhood-level images are captured with sufficient overlap such that each area of interest is typically covered by at least two oblique images from each compass direction captured, and such that opposing compass directions provide 100% overlap with each other. Approximately one hundred (100) oblique area images are captured per sector.

It should be particularly noted that capturing oblique community and/or neighborhood-level images from all four compass directions ensures that every point in the image will appear in the foreground or lower portion of at least one of the captured oblique images, where ground sample distance is lowest and image detail is greatest.

In the embodiment shown, image-capturing and geo-locating system30includes a gyroscope, compass and altimeter. However, it is to be understood that the image-capturing and geo-locating system of the present invention can be alternately configured, such as, for example, to derive and/or calculate altitude, pitch, roll and yaw, and compass heading from the GPS and INU signals/data, thereby rendering one or more of the gyroscope, compass and altimeter unnecessary. In fact,

In the embodiment shown, image-capturing devices are at an equal angle of declination relative to a horizontal plane. However, it is to be understood that the declination angles of the image-capturing devices do not have to be equal.

In the embodiment shown, image-capturing computer system executes image and data acquiring software that issues a common or single image-capture signal to the image-capturing devices to thereby cause those devices to acquire or capture an image. However, it is to be understood that the present invention can be alternately configured to separately cause the image-capturing devices to capture images at different instants and/or at different intervals.

In the embodiment shown, the method of the present invention captures oblique images to provide double coverage of an area of interest from paths/perspectives that are substantially opposite to each other, i.e., 180° (one-hundred and eighty degrees) relative to each other. However, it is to be understood that the method of the present invention can be alternately configured to provide double coverage from paths/perspectives that are generally and/or substantially perpendicular relative to each other.

While the present invention has been described as having a preferred design, the invention can be further modified within the spirit and scope of this disclosure. This disclosure is therefore intended to encompass any equivalents to the structures and elements disclosed herein. Further, this disclosure is intended to encompass any variations, uses, or adaptations of the present invention that use the general principles disclosed herein. Moreover, this disclosure is intended to encompass any departures from the subject matter disclosed that come within the known or customary practice in the pertinent art and which fall within the limits of the appended claims.