Patent Application
20080059065
Features of the present invention will become apparent to those skilled in the art from the following description with reference to the drawings. Understanding that the drawings depict only typical embodiments of the invention and are not therefore to be considered limiting in scope, the invention will be described with additional specificity and detail through the use of the accompanying drawings, in which:
In the following detailed description, embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that other embodiments may be utilized without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.
The present invention relates to a method and system for navigation of an unmanned aerial vehicle (UAV) in an urban environment. The present method and system are useful in GPS-denied navigation of a UAV. In general, the present method employs an initial UAV fly-over of an urban terrain at a higher altitude that will later be traversed at a lower altitude in the urban canyon. During the initial fly-over, GPS-tagged images are captured, and these images are stitched into a GPS-aided image mosaic. During the subsequent lower altitude flight in the urban canyon, images captured by the UAV camera can be matched to the fly-over image mosaic, and the current position of the UAV relative to GPS-aided positions used to acquire the fly-over image mosaic can be calculated. This results in a determination of the absolute position of the UAV at about the same accuracy as the GPS-aided positions originally used to construct the image mosaic.
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The present navigation approach differs from referencing to a satellite image in that the UAV acquires its own reference imagery during a preliminary flight. An advantage of the present approach is the temporal and spatial proximity of the acquired fly-over image mosaic to the images the UAV will later capture while navigating in the urban environment.
A second set of images is captured (block 230) in a subsequent fly-over of the urban environment at a second altitude that is lower than the first altitude. The second set of images are non-GPS-tagged images. During the subsequent fly-over, image features from the image mosaic are matched with image features in the non-GPS-tagged images (block 240). A current position of the UAV relative to the GPS-aided positions is then calculated (block 250) based on the matched image features.
The present method automatically establishes the correspondences between the images in the fly-over image mosaic and the current images (non-GPS-tagged) of the UAV. This automatic procedure overcomes differences in lighting, view angle, the scene (e.g., cars parked or moved), and particularly scale between the mosaic images and the current images of the UAV. This can be accomplished by combining (1) an inertial position estimate of the UAV to get a prior distribution and initial estimate for possible matches between the mosaic images and the current images, and (2) cueing based on salient image features to “spontaneously” notice matches between the mosaic images and the current images. A variety of salient image feature types can be considered depending on the exact scenario.
The present method can be implemented by utilizing computer hardware and/or software, which provide a means for stitching the captured GPS-tagged images together into an image mosaic using the GPS-aided positions, a means for matching image features from the second set of images with image features from the image mosaic, and a means for calculating a current position of the unmanned aerial vehicle relative to the GPS-aided positions based on the matched image features.
Instructions for carrying out the various process tasks, calculations, control functions, and the generation of signals and other data used in the operation of the method and systems described herein can be implemented in software, firmware, or other computer readable instructions. These instructions are typically stored on any appropriate computer readable media used for storage of computer readable instructions or data structures. Such computer readable media can be any available media that can be accessed by a general purpose or special purpose computer or processor, or any programmable logic device.
Suitable computer readable media may comprise, for example, non-volatile memory devices including semiconductor memory devices such as EPROM, EEPROM, or flash memory devices; magnetic disks such as internal hard disks or removable disks; magneto-optical disks; CDs, DVDs, or other optical storage disks; nonvolatile ROM, RAM, and other like media. Any of the foregoing may be supplemented by, or incorporated in, specially-designed application-specific integrated circuits (ASICs). When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, the computer properly views the connection as a computer readable medium. Thus, any such connection is properly termed a computer readable medium. Combinations of the above are also included within the scope of computer readable media.
The method of the invention can be implemented in computer readable instructions, such as program modules or applications, which are executed by a data processor. Generally, program modules or applications include routines, programs, objects, data components, data structures, algorithms, etc. that perform particular tasks or implement particular abstract data types. These represent examples of program code means for executing steps of the method disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps.
The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is therefore indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
