| 主权项 |
1. An apparatus comprising:
at least one processor; and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to: acquire information indicating first indoor magnetic field vectors measured by a first portable device inside a building; generate a first indoor magnetic field sequence, IMFS, on the basis of the first indoor magnetic field vectors; acquire information indicating second indoor magnetic field vectors measured by a second portable device inside the building; generate a second IMFS on the basis of the second indoor magnetic field vectors, wherein the first and the second IMFSs represent at least one of the magnitude and the direction of the Earth's magnetic field; acquire information indicating the geographical location of the first portable device and the second portable device, wherein the geographical location is based on at least one of the following techniques: a radio frequency based location, a global positioning system; determine a building or a geographic area, among a plurality of buildings or geographic areas, in which the first portable device and the second portable device are on the basis of the indication of the geographical location; if the first portable device and the second portable device are in the same building or in the same geographic area, perform a comparison between at least part of the first IMFS and at least part of the second IMFS; characterize a certain path, which the first portable device has traversed, with the first IMFS; identify a specific portion of the first IMFS; and detect, based on the comparison, that the second IMFS comprises substantially the same specific portion as the first IMFS, thereby determining that the second portable device is or has been at a same location in the building as the first portable device. |
