CROSS-REFERENCE TO RELATED APPLICATIONS
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This application is a divisional of pending U.S. application Ser. No. 12/059,865 entitled “POSITION ESTIMATION FOR NAVIGATION DEVICES,” filed Mar. 31, 2008, which is incorporated herein by reference.
GOVERNMENT INTEREST STATEMENT
The U.S. Government may have certain rights in the present invention under contract No. HDTRA-06-6-C-0058, subcontract No. CHI-06022-001 as awarded by the Defense Threat Reduction Agency.
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Reliable navigation systems and devices have always been essential for estimating both distance traveled and position. For example, early navigating was accomplished with “deduced” or “dead” reckoning. In dead-reckoning, a navigator finds a current position by measuring the course and distance the navigator has moved from some known point. Starting from the known point, the navigator measures out a course and distance from that point. Each ending position will be the starting point for the course-and-distance measurement. In order for this method to work, the navigator needs a way to measure a course and a way to measure the distance traveled. The course is measured by a magnetic compass. In pedestrian dead reckoning, the distance is the size of a single step. A position estimate is derived by the integration of distance and direction over a sequence of steps. This type of navigation, however, is highly prone to errors, which when compounded can lead to highly inaccurate position and distance estimates.
In more advanced navigation systems, such as an inertial navigation system (INS), positional errors can accumulate over time. For example, any navigation performed in areas where satellite or radar tracking measurements are inaccessible or restrictive (such as areas where global positioning system, or GPS, measurements are “denied”) is susceptible to the accumulation of similar positional errors. Moreover, in the dead-reckoning methods discussed above, these positional errors accumulate based on the distance traveled. There is a need in the art for improvements in position estimation for navigation devices.
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The following specification provides for at least one method of position estimation for navigation devices using sensor data correlation. This summary is made by way of example and not by way of limitation. It is merely provided to aid the reader in understanding some aspects of at least one embodiment described in the following specification.
Particularly, in one embodiment, a method of providing position estimation with a navigation device comprises periodically recording magnetic field strength of an area substantially surrounding a navigation device as a user of the navigation device traverses a select pathway. The method combines the recorded magnetic field strength with measurements from at least a dead reckoning portion of the navigation device to provide position estimates along the select pathway. The method further corrects each of the position estimates from a starting position on the select pathway, where each of the corrected position estimates have an error value below one or more previous position estimates and any intervening positions between each of the one or more previous position estimates and the starting position, with the error value corresponding to an error threshold based on the previous position estimates.
These and other features, aspects, and advantages are better understood with regard to the following description, appended claims, and accompanying drawings where:
FIG. 1 is a block diagram of a navigation device;
FIGS. 2A and 2B are traversing diagrams of navigating in a select pathway;
FIG. 3A is a traversing diagram of navigating in a select pathway prior to position correction;
FIG. 3B is a traversing diagram of navigating in the select pathway of FIG. 3A after position correction;
FIG. 4A is a traversing diagram of a select pathway with at least one marked position before sensor data correlation at a selected position;
FIG. 4B is a traversing diagram of navigating in a select pathway showing one or more positions that correlate with the marked position of FIG. 4A;
FIG. 4C is a traversing diagram of navigating in the select pathway of FIG. 4B after the correlated positions have been corrected;
FIG. 5A is a traversing diagram of navigating in a select pathway using a navigation device indicating the positions which are correlated;
FIGS. 5C is the azimuth data and 5B is the calculated correlation function diagram from the navigation device of FIG. 5A;
FIG. 6A is a traversing diagram of navigating in a select pathway using a navigation device having at least one marked position and one or more correlated positions;
FIGS. 6B and 6C are calculated correlation data diagrams for sensor data channels from the navigation device of FIG. 6A;
FIG. 7 is a diagram in graphical form illustrating product correlation as provided by the correlation data of FIGS. 6B and 6C;
FIG. 8 is a flow diagram of a method for providing position correction in a navigation device;
FIG. 9 is a flow diagram of a method of correlating position measurements in a navigation device;
FIG. 10 is a flow diagram of a method of qualifying navigation data from the navigation device of FIG. 9; and
FIG. 11 is a flow diagram of a method of correlating position measurements in a navigation device.