The origin of lamella is from the Latin language. In Architecture it is a piece of metal, lumber or concrete that crosses to keep a roof structure in place. In anatomy it is a fragile layer of calcium that assists the formation of bones.

The position of Lamella is the Middle

This is not a straightforward question. It's not too hard to develop an Excel spreadsheet parameterized by the width and length of the space to be covered, and the height of the roof, but there are other significant elements like the thickness of the lamella and the nature of the connectors. The basic idea is that each lamella arch is circular in section, with an integral number of lamellas, skewed with respect to the orientation of the space. Then each of the, say, n lamellas subtends an angle equal to 1/n of the angle subtended by the whole arch, so its unadjusted length is easy to calculate.

Yes, the word lamella is a noun, a singular (the plural is lamellae), common, concrete noun.

lamella