code: func (lh *LocationHelper) PermanodeLocation(ctx context.Context, permaNode blob.Ref,
  	at time.Time, owner *Owner) (camtypes.Location, error) {
  	return lh.permanodeLocation(ctx, permaNode, at, owner, true)
  }
docs: // PermanodeLocation returns the location info for a permanode,
  // from one of the following sources:
  //  1. Permanode attributes "latitude" and "longitude"
  //  2. Referenced permanode attributes (eg. for "foursquare.com:checkin"
  //     its "foursquareVenuePermanode")
  //  3. Location in permanode camliContent file metadata
  // The sources are checked in this order, the location from
  // the first source yielding a valid result is returned.