The thing is that location 'signatures' can be created from many types of sensors, as long as they're able to record an environmental factor that is discriminab

The thing is that location 'signatures' can be created from many types of sensors, as long as they're able to record an environmental factor that is discriminable on a position. It's not important that the signature is very accurate in itself, only that enough independent signatures can be combined together to make one accurate estimate.