Why this page exists. A phone photo carries GPS and a focal length but
no compass bearing — 29 reference photos, zero headings. GPS puts you on a
dot; a street has two sides. This records the bearing at the moment you shoot, so
the renderer knows which way you were looking.
Not the same thing: the Geolocation API's coords.heading is your
course over ground and is null when you stand still — which is exactly
when you take a photo. The real bearing comes from the device orientation sensors,
and both are recorded separately here so they can never be confused.