Applying indoor magnetic fields for acquiring movement information

A method for acquiring information about relative movements of portable devices indoors, the method comprising:

• utilizing at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code being configured, with the at least one processor, 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;
• perform a comparison between at least part of the first IMFS and at least part of the second IMFS;
• and
• acquire information on the relative movement of the first portable device with respect to the second portable device inside the building on the basis of the comparison result.

A computer program product embodied on a non-transitory distribution medium readable by a computer and comprising program instructions which, when loaded into an apparatus, execute the method comprising:

• acquiring information indicating first indoor magnetic field vectors measured by a first portable device inside a building;
• generating a first indoor magnetic field sequence, IMFS, on the basis of the first indoor magnetic field vectors;
• acquiring information indicating second indoor magnetic field vectors measured by a second portable device inside the building;
• generating 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;
• performing a comparison between at least part of the first IMFS and at least part of the second IMFS;
• and
• acquiring information on the relative movement of the first portable device with respect to the second portable device inside the building on the basis of the comparison result.