how measuring wheel encoder work

hey everyone

Google didnt help me so I just wanted to know how a measuring wheel encoder works.How is it used in applications such as a cut to length applications.I have a steel profile and a blade cuts according the length set. So basically i want to know how motion is converted to measure length. please forgive if this is basic

The circumference of the wheel is machined precisely (for example 1/4 meter). This is attached to the encoder so that one revolution of the encoder equals one of the circumference units. In my example 4 revolutions would be 1 meter. Special mounts, usually involving hold down springs or weights, ensure that the wheel is in good contact with the item to be measured. From there it is simply mathematics within the controller. The wheel must be inspected at intervals to check for wearing which may affect the accuracy of the measurements. Precise measurements during high acceleration or deceleration may occur due to slipping.

encoder basic's

http://www.encoder.com/literature/installation-wiring-guide.pdf

fire optic cable industry and Weaving industry use encoder with one measuring wheel .also like driving sheave use in the elevator industry.turn circumference to distance.
www.simre.com.cn

Why not use mesauring laser cel units instead?
The prices for small distance units are almost the price of encoders with many advantages. Sick has good models.

Which Sick laser sensor are you recommending, and how would it work as a replacement for a measuring wheel in a cut to length application?

I've trialled a laser doppler velocity meter for a similar application, does the job, but expensive ($10000Au was the cheapest I found). There are a few CCD camera based velocity sensors hitting the market as well, but I'm keen to hear of other (economical) options to replace a conventional measuring wheel/encoder setup.