Concepts: Camshaft vs. Crackshaft Position Sensor?

General Discussion
1

I am just diving back into cars after many years.
Trying to fill in gaps of conceptual knowledge.

I understand that these 2 sensors are part of a fuel injection system.
It is no longer purely mechanical with lifters, rocker arms, valves, etc.

What is the difference between them?
I have read they both are used to determine when to fire the spark plug.
(Something the timing belt used to do?)

Can you share the basic concepts behind these 2 sensor’s roles?

2

A crackshaft has a street value which is higher than the cost to manufacture. The police have great leeway when assigning value.

3

Here ya go. This explains it beautifully.
http://www.aa1car.com/library/crank_sensors.htm