I’ve managed to do reverse engineering of circuit boards using GIMP and rough alignment of layers using images like the one pictured. I want to use images to reverse engineer parts in CAD, but the minor lens distortion of a camera on a phone at ~20cm high on top of a stack of objects to keep it eyeballed flat is not enough. The result is off in multiple planes. There are minor errors in my curves in the transparent CAD part pictured, but the hole pattern is correct. The picture has been calibrated to 20mm against the ruler. Any suggestions on how to make this usable for replicating the ellipse that crosses the holes ±0.05mm?
As others have said, using a flat bed scanner will save some work. If you need to photograph it though:
Use paper with grid lines as background (not sure the name, used to use it in maths at school). This will give you not just an index for scale but also for ‘squareness’.
Position camera perpendicular to subject
Use a telephoto or zoom lens from a distance rather than wide angle from close up to minimise lens distortion.
Import image into GIMP or photoshop and use rulers, guides and transform tools to scale the image correctly and make it perfectly square.
Matching the colour perfectly is more complicated and I won’t go into that here.
Let me know if you need any more tips. I photograph a lot of artwork and documents.
To build if you’re doing this a lot and can’t use a brand lens with known correction data in darktable, set up graph paper and phone camera on a tripod to keep everything consistent, then photograph the empty paper. Create a transform in gimp to make the paper completely flat / square, and then just reapply that transform for every object you need to capture.