This is a really cool solution to indoor mapping/positioning using differences in magnetic fields within a building. Currently, it’s designed for utilizing the sensors in smartphones but this could be ported to NETMF once it takes off.
As far as being clever, yes and no as while magnetic fields exist, they also can change for all sorts of reasons, for example a minor layout change or even stock level change (in say canned goods) in the store and you might need to redo the map. I remember we tried to do something similar with the HTC HD2 and build a metal detector using changes in magnetic deviations, still it was interesting.
I tend to agree with @ Duke Nukem, and you would need to take into account power fluctuations as well. A novel idea.
@ Duke - They claim to be measuring differences in the fields due to the metal structure of the building. I realize that the items within the structure obviously would cause their own changes but I wonder if they can be filtered out when compared to the mass of steel used to build large structures. Also, if the smartphone software were bi-directional then it could actually update the map with new measurements as people walked about since there would almost always be good points on either side of a changed area. This is all speculation but I think it’s the way I would do it