How does quoting from scanned drawings work?

Why is a scan a different problem from a native drawing?

A vector PDF or DXF already contains lines, arcs and text as structured objects. A scan or photograph contains none of that: it is a grid of pixels, and a line only exists because a row of pixels happens to be dark. Every downstream step has to earn back structure that a native file already had.

What happens before anything can be measured?

The page is deskewed, since a scan is rarely perfectly square, using the detected border or text-line angle to rotate it true. It is then denoised, removing speckle, fold lines and scan artefacts that would otherwise be misread as geometry, and binarised into clean line art so edges can be traced. A resolution check runs alongside this: below a usable DPI, fine dimension text and thin lines are not reliably recoverable, and the page is flagged rather than guessed at.

Only after this cleanup does the page get split into regions, the title block, the dimension and notes area, and the drawing views, because each region needs different treatment from here on.

How does text get read differently from geometry?

Title block fields, dimensions and notes go through OCR tuned for the kind of text they are: part numbers and materials as general text, dimensions and tolerances with numeral and symbol recognition. A feature that must be measured rather than read as printed text, a bend or a hole diameter, is instead estimated from the traced raster line work, and that estimate carries a lower confidence than the same feature would get from a native vector or 3D file, because it started from pixels rather than exact geometry.

How are handwritten notes and redlines handled?

Stroke weight and consistency distinguish a handwritten annotation from the original printed drawing, so a redline is treated as a separate note on the job rather than silently merged into the original geometry. Anything that would change a price based on a handwritten mark waits for a person to confirm it against the source region first.