In my case (in Ohio) it was low flying aircraft measuring the distance and an officer at the side of the road waving me to pull over based on the results (along with several other drivers and a patrol car at the side for those who chose not to stop...).
I was pretty bothered by what I saw as a cheap stunt for money, so I went to court on the principal of it, after reading up on speeding ticket defense and the city's speed ordinance at the local University Library. Present at the hearing was the officer at the side of the road and the assistant city prosecutor. Here's a nut-shell of how it went:
Prosecutor to police officer: How fast was the defendant going?
Officer: The defendant was clocked at --
Me: Objection, your honor.
Judge: Yes, young man?
Me: The officer doesn't know how fast I was going. Based on the complaint issued to me in writing here, he was relying on an aircraft pilot's measurements. The pilot is not here; that makes the officer's testimony hearsay.
(Prosecutor approaches Judge after talking with officer)
Judge: Young man, would you agree to an extension 10 days from now until the pilot can be summoned?
Me: Respectfully, no, your honor. That date would put the hearing beyond the 30 day time-line for disposal of this case, which is the end of this week.
Judge: young man, would you like your case dismissed?
Me: yes, your honor.
Judge: case dismissed.
Know the basics of the law in your case. Sometimes it can end up being on your side, as long as your willing and able to take the time to research it and appear in court.