What is the scope of the implied invitation of a police officer to enter the curtilage of a house?

"'"It is clear that police with legitimate business may enter areas of the curtilage which are impliedly open, such as access routes to the house. In so doing they are free to keep their eyes open. [Citation.] An officer is permitted the same license to intrude as a reasonably respectful citizen. [Citation.] However, a substantial and unreasonable departure from such an area, or a particularly intrusive method of viewing, will exceed the scope of the implied invitation and intrude upon a constitutionally protected expectation of privacy. [] What is reasonable cannot be determined by a fixed formula. It must be based on the facts and circumstances of each case. [Citation.]"' (People v.

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