What is the test for a stop by a police officer in a motor vehicle stop?

"The idea that an assessment of the whole picture must yield a particularized suspicion contains two elements, each of which must be present before a stop is permissible." (United States v. Cortez, supra, 449 U.S. 411, 418, 101 S.Ct. 690, 695.) The first is that the assessment must be based on all of the circumstances, including objective observations, information from police reports, and "consideration of the modes or patterns of operation of certain kinds of lawbreakers." (Ibid.) From these data, the court said, a trained police officer could draw inferences "that might well elude an untrained person." (Ibid.)