1. A method, comprising: dynamically generating in a mobile wireless device, grid nodes representing two or more floor areas in an enclosed space, based on a map of the enclosed space; estimating in the mobile wireless device, locations along a path of motion of a user of the mobile wireless device traversing the two or more floor areas, based on motion observations made by a motion sensor in the mobile wireless device and map information; generating a radiomap of the two or more floor areas by making radio measurements at time instances with the mobile wireless device, at the estimated locations along the path of motion, and mapping the measurements to the generated grid nodes that are closest to the estimated locations; compiling in the mobile wireless device, a three dimensional fingerprint data structure of the radiomap of the two or more floor areas, including observation elements representing the radio measurements made at the time instances at the mapped grid nodes; repeating making radio measurements at later time instances with the mobile wireless device, at locations along a repeated path of motion of the user of the mobile wireless device repeating a traverse of the two or more floor areas, based on motion observations made by the motion sensor in the mobile wireless device along the repeated path of motion; and combining in the mobile wireless device, the repeated radio measurements made at the later time instances, with the radio measurements represented by the observation elements of the three dimensional fingerprint data structure of the radiomap, to learn a refined radiomap of the two or more floor areas.