Road Fan

It's not brain surgery, but some of us want to understand the details and perhaps to design our own ideal frame. That requires accuracy better than the supposed 5% tolerance. I can't even accept that is an "industry tolerance," anyway. One framebuilder, an alignment fanatic, that I've spoken to says he is struggling to build so the frame tubes are actually where he wants them when he's done. He doesn't want to have to hand-align each frame so much.

Scooper

For me, the beauty of laying down the frame on paper full scale using tube intersections, dropout centers, and BB center as reference points is that I don't have to worry about the frame being level, camera parallax, or anything else. It is what it is, and precise measurements can be made from the drawing. WYSIWYG.

As I said, the downside is that's labor intensive.

mkael

I have copied photographed drawings a few times. Photo taken very close by a camera with big visible distortion just to the naked eye. Photo not really taken exactly from above. Things were distorted but I knew the lengths of certain things on the photographs. How long do they measure and how long they are in reality. For something I needed the length I measured the closest thing I knew the real length of. No matter if horizontal or vertical. Then compared the ratios of known and wanted lengths and calculated. Later I saw it was surprisingly accurate using this rough method.

I am certain there are real mathematical functions for this. I remember I did some nice multiphoto panoramas with hugin and autopanosift??? a few years back and the problems doing that are exactly the same as here.
https://hugin.sourceforge.net/tutoria...ctive/en.shtml Maybe something to look into

Mark something on the bike so you know the length exactly. Horizontally and vertically mark something somehow. Use the tube lengths as reference. Calculate degrees with trig functions. Just taking horizontal and vertical distortions into account. If you have a good photograph I think it will be extremely accurate. I think the biggest issue for error will be getting up the fork in a line with the frame then.

Scooper

If you're scaling off of a photograph, one tool that really simplifies the process is the Gerber Variable Scale.

Assuming the photograph is taken with minimizing distortion in mind (taken directly from the side of the bike at a distance using a long telephoto lens), adjust the scale to show the value of a known distance on the frame, e.g. the length of the seat tube from the crank center to the top of the seat tube, and then all the other dimensions on the photo can be measured directly from the photo using the scale.