1. A method of determining a position estimate for a wireless terminal, comprising: obtaining, via a first receiver, an initial position estimate for the terminal; obtaining, via at least one of the first receiver or a second receiver distinct from the first receiver, at least a partial set of measurements from one or more position determination systems having a higher level of accuracy over a position determination system for the initial position estimate; and updating the initial position estimate with the partial set of measurements to obtain a revised position estimate for the terminal, wherein the updating includes: deriving a measurement vector based on the initial position estimate and the partial set of measurements, forming an observation matrix for the set of measurements, deriving a correction vector based on the measurement vector and the observation matrix, and updating the initial position estimate with the correction vector.