Aspects of the subject disclosure may include, for example, a process that formulates an inference that a first group of mobile devices are at ground level, and obtains, for the first group of mobile devices, positions and barometric pressure readings. Ground heights with respect to a common reference height are determined for the first group of mobile devices, and reference barometric pressures are calculated for the first group of mobile devices, at the common reference height according to the barometric pressure readings and the determined ground heights. At least a portion of the reference barometric pressures are combined to obtain a reference barometric pressure. Other embodiments are disclosed.