Track model constraint for GPS position
a track model and constraint technology, applied in the field of track models, can solve the problems of large time error, inability to provide a comparable clock in a receiver, and large time error
Inactive Publication Date: 2003-02-20
FORD THOMAS J +3
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AI Technical Summary
Benefits of technology
The track model significantly improves positioning accuracy, often by a factor of 10, with enhanced horizontal accuracy and faster ambiguity resolution, even in conditions with poor satellite geometry, by providing a more robust navigation solution.
Problems solved by technology
GPS satellites use very accurate and stable atomic clocks, but it is economically infeasible to provide a comparable clock in a receiver.
Note that t.sub.rcve is measured according to the receiver clock, which may have a large time error.
There are a number of errors that are associated with GPS ranging, including errors due to the Earth's ionosphere and atmosphere, noise, multipath satellite clock, and ephemeris errors.
Additionally, basic geometry itself can based on the configuration of the satellites in the sky can magnify the errors.
So, if two receivers are fairly close to each other, the signals that reach both of them will have traveled through virtually the same slice of atmosphere, and will have virtually the same errors.
Despite the use of differential GPS, many land applications which use GPS are hampered by the restrictions imposed by buildings and natural impediments to the transmitted GPS signals.
Often the GPS geometry is too poor to provide the geometrical strength required to generate the position accuracy that an application requires.
One particular example of an environment for which the above described GPS technology does not provide sufficient accuracy and reliability is the real-time tracking of automobiles (or other objects) during a race, which requires extreme positioning accuracy and reliability in conditions of reduced satellite visibility and a highly dynamic environment.
In an environment such as a professional auto race, the visibility of all satellites is severely reduced at some point on the track due to the existence of obstacles such as a grandstand.
Additionally, the availability of satellites is reduced and the remaining signals are corrupted by the proximity of objects such as a 10 meter tall overhanging steel and wire fence on the outside edge of the track.
Typically, the tracks are not level and the cross track slope is not constant (varying by as much as 35 degrees between the straight sections and the curves), all of which further degrade GPS accuracy and reliability.
In many land and air applications, such constraints are not particularly useful for navigation because the constraints are often not accurate enough to significantly strengthen the navigation solution.
However, in the track model constraint process the constraint position and covariance (or weight) matrix change at almost every positioning epoch, and the constraining planes are not necessarily parallel to the local level plane.
This could be satisfied if the internal position was transformed to geographic co-ordinates, but this transformation is time consuming, and it is possible that it may have to be carried out more than once per solution.
There are more complications if the knowledge of height is to be represented by this system.
If the base station coordinates are in error relative to the relevant frame, then there will be a reported mismatch between the items in the true ECEF frame and the ECEF positions reported by the receiver.
Method used
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has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
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A track model is created for use with a GPS receiver. In one embodiment, the track model is a set of planar surfaces which approximate the contiguous surface on which navigation takes place. The GPS receiver searches for an appropriate planar surface associated with its approximate position. Having found the appropriate planar surface, the GPS receiver constrains its position using the planar surface associated with its approximate position. Using the track model improves the accuracy of the computed position at the time and improves the ambiguity estimation process so that positions with greatly improved accuracy are available sooner.
Description
[0001] This application claims the benefit of U.S. Provisional Application No. 60 / 213,684, "Locating an Object Using GPS With Additional Data," filed on Jun. 23, 2000; and U.S. Provisional Application No. 60 / 295,310, "Track Model Constraint Enhancement For GPS Receiver," filed on Jun. 1, 2001; both of which are incorporated herein by reference.[0002] 1. Field of the Invention[0003] The present invention is directed to the use of a track model to constrain a GPS position.[0004] 2. Description of the Related Art[0005] Technologies for tracking moving objects are in demand. For example, systems are used to track airplanes, automobiles, persons, objects at sporting events and other objects of interest. One technology that has become popular for tracking objects is the use of the Global Positioning System (GPS). GPS is a satellite based navigation system operated and maintained by the U.S. Department of Defense. GPS consists of a constellation of GPS satellites providing worldwide, 24 ho...
Claims
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IPC IPC(8): G01C21/28G01S1/00G01S5/00G01S5/14G01S19/49G01S19/50
CPCG01C21/28G01S5/0027G01S5/0036G01S5/0054G01S19/04G01S19/50
InventorFORD, THOMAS J.FENTON, PATRICK C.MCGUFFIN, JAMES O.HONEY, STANLEY K.
OwnerFORD THOMAS J