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Abstract

A method, implementable on a computer, for filtering time-varying location solution coordinates P.sub.x,n, P.sub.y,n, and P.sub.z,n, determined by a Satellite Positioning System (SATPS, usually GPS or GLONASS), which operates in a static mode and a dynamic mode, to reduce large discontinuities and control the rate at which a changing sequence of measurement errors can induce a change in a sequence of location solutions. As an initial step, SATPS location solutions P.sub.x,n, P.sub.y,n, and P.sub.z,n, and SATPS velocity solutions V.sub.x,n, V.sub.y,n, and V.sub.z,n are generated for selected fix times t=t.sub.n with essentially no time lag in these solutions, when recent measurements are available from all satellites in the solution constellation. Sequences of filtered location coordinates {P.sup..LAMBDA..sub.x,n }, {P.sup..LAMBDA..sub.y,n }, and {P.sup..LAMBDA..sub.z,n } are formed, to reduce discontinuities that occur with a changing set of measurement errors caused by one or more of the following perturbing events: (1) change of the satellites in the SATPS solution constellation, (2) change of the location solution from a three-dimensional solution to a two-dimensional solution, (3) change of the location solution from a two-dimensional solution to a three-dimensional solution, (4) change in availability of differential SATPS info, (5) appearance or disappearance of Selective Availability, (6) appearance or disappearance of receiver noise in satellite measurements, (7) appearance or disappearance of multipath signals in satellite measurements, and (8) a significant change in a latency error for any location or velocity coordinate of the solution. Filtered location coordinates P.sup..LAMBDA..sub.x,n, P.sup..LAMBDA..sub.y,n, and P.sup..LAMBDA..sub.z,n are formed as linear combinations, using selected weights, of the unfiltered location solutions P.sub.x,n, P.sub.y,n and P.sub.z,n with predicted location coordinates P.sup..LAMBDA..sub.x,n.sup.-, P.sup..LAMBDA..sub.y,n.sup.- and P.sup..LAMBDA..sub.z,n, using the average velocities (V.sub.x,n +V.sub.x,n-1)/2, (V.sub.y,n +V.sub.y,n-1)/2 and (V.sub.z,n +V.sub.z,n-1)/2 in the time interval t.sub.n-1 .ltoreq.t.ltoreq.t.sub.n between two location fix times t.sub.n.

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First Claim