1. A method for computing position in a receiver, comprising: obtaining pseudorange measurements at a location, with a circuit of the receiver; determining a speed of the receiver; comparing the speed of the receiver to a threshold value; and if the speed of the receiver is below the threshold value, obtaining from a regional-terrain model altitude information associated with a modeled region, wherein the location is in a vicinity of the modeled region; and computing a position as a function of the pseudorange measurements and the altitude information, wherein obtaining from a regional-terrain model altitude information comprises obtaining from the regional-terrain model an altitude and an altitude uncertainty.