The "open skies" or aerial surveillance cases have their origin in the "open fields" doctrine, which held that police can enter without a warrant a piece of land outside the curtilage of a home as it is an "open field." Airborne observation of residential curtilage without a warrant is constitutional if such methods are available to the public and are not sufficiently rare to suggest a reasonable expectation of privacy. It remains undecided whether sophisticated photography, permissible without a warrant applied to an outdoor business area, can be used to photograph residential curtilage without a warrant.