TechnoAware is the only option that has a potential solution?
Unfortunately it was looking so, but luckly also AgentVi replied to you so I suppose you are more relieved now.....;))
Jokes aside, I have actually not understood which one of the following possible 2 options does your Customer need:
1) To have a status of each parking lot (occupied/free) in order, for example, to give to the user an information about where to go to park
or
2) To have "just" an estimation about the amount of free parking lots in that moment, but without caring about which specific one is free or not
In the first case you need something able to monitor and detect the status of the specific parking lot (the module I was writing about). Just a flow counting of course can't help in this case.
In the second case instead, or you could use the same above one as well; or, to save cameras, you can actually use a module counting the entry/exit of cars, as AgentVi correctly suggested (by the way: also us, we have the function Counting for that purpouse..). But beware, because the counting of cars when for example it's dark with the headlights on (since late afternoon to early morning) it's still a pretty challenging stuff, if using optical cameras. And when you go even little wrong in an aggregated flow counting at-the-gates, you might risk to accumulate a big error in the inside counting estimation.
Cheers,
Simone
[TechnoAware]