I wanted to give this question some love.
Linear pricing -- for those not in the know -- is a pricing model based on the number of units (inches, feet, centimeters, meters, etc.) that are used to make up the large-format print job. For example, if I print an 18" x 120" banner on a plotter loaded with 24" paper, linear pricing per foot would render $n/ft * 10ft = $n10, assuming "n" is some value...3, 4, 5, whatever...so $5 x 10 = $50.
The fundamental problem with an automatic charging model is consistency, and that occurs in any solution that claims to charge by the linear foot."Huh? Whaddya mean, 'consistency'?" Let me explain. If I'm in the plotter driver's Properties page, and I'm printing that poster, I have the choice of many different paper sizes, and some offer suffixes: SEF, LEF, or something similar. SEF is "Short Edge Feed," meaning that the smallest edge of the poster feeds first (almost like a "Portrait" setting, but don't get too comfortable there), and LEF is "Long Edge Feed" which feeds, you guessed it, the long edge of the poster first. But look at what happens in the model:
It's the same size poster, but one will charge at (let's say it's an ARCH-D poster) 36 inches (SEF), and the other at 24" (LEF). But 36" wide paper (depending on supplier; I used Staples) can be 70% more expensive per roll than 24" paper. So now you're managing a 24" roll linear price and a 36" roll linear price to keep your head above water, because a flat $5 per foot makes the SEF output $15 and LEF output $10, but your real cost per poster is heavier in the reverse direction. A representative Cost Model dialog box may look like this:
Within Uniprint, the challenge then becomes taking the Page Counter's document size and ensuring that the dimensions make sense for the cost model defined for the device. I see it quickly becoming a manual process, requiring a Cashier equivalent to set the job's cost based on the attributes available in Pharos Administrator and then releasing it to the appropriate device just to keep things on the level, much like third party/service bureaus do.
On the flip side, when printing based on paper size (like ARCH-D), the single cost is the same no matter how the paper is fed, allowing for a consistent job cost.
I hope this helps?