Positioning based on illumination sources

A method comprising:

• A) at a first location, using a camera of a mobile device to capture a first image in which a first illumination source appears;
• B) by reference to the first illumination source as appearing in the first image, determining first heading information of the mobile device;
• C) as the mobile device moves from the first location to a second location, using one or more inertial sensors of the mobile device to extrapolate from the first heading information and from first position information of the mobile device to generate a plurality of extrapolated first candidate locations of the mobile device and a plurality of respective extrapolated first candidate headings of the mobile device;
• D) at the second location, using the camera of the mobile device to capture a second image in which a second illumination source appears, wherein the second illumination source does not appear within field of view of the camera until the mobile device has reached the second location from the first location;
• E) by reference to the second illumination source as appearing in the second captured image, determining a plurality of second candidate locations of the mobile device, and a plurality of respective second candidate headings of the mobile device;
• and
• F) based on a comparison of the extrapolated first candidate locations and headings with the second candidate locations and headings, determining at least one estimated location and respective heading of the mobile device.