How to scale mesurements of a bike frame from a photo?

[slope]

I have a manufacturers' photo of a bicycle, seemingly at 90º to side on. How can one take measurements from said photo, of seat tube length and head tube length and extrapolate those to my saddle height, to see where the handlebar height would be in relation to my saddle height? Also would be real good to extrapolate the saddle nose horizontally to the centre angle line of the handlebar stem

This photo is either a M or L frame (To my eye/guess, it looks probably like a M?)

The M frame has a seat tube* of 490mm and a head tube length of 145mm

The L frame has a seat tube* of 540mm and a head tube length of 170mm.

My saddle height, from BB centre to the top of my saddle is 740mm as measured along the centreline of the seat tube and seat pin to the top of the saddle.

I used to have Photshop before it went subscription only - and seem to remember this sort of calculation could be done reasonably easily using its 'measurement tool'?

I now have Affinity Photo and still use a modern iMac.

*presumably that means the usual BB centre to bottom of seat tube clamp?

OOPS! Photo coming in a couple of minutes Clicky for larger version


https://www.boardmanbikes.com/Assets/User/20215-BI_HYB_8.9_Electric_Bike.jpg

[Lightning Phil]

Assuming the (L) 540mm is also measured from centre of BB, then your seat post will stick out 740mm - 540mm = 200mm = 20cm. For a 300mm seat post that leaves 100mm inserted which will be safe. 

Edit you’d need the seat tube angle relative to vertical or horizontal plus length of down tube to work out relative heights and assuming rise from stem in minimal. Then it’s just trigonometry from schooldays.

[slope]

Thanks Lightening Phil - seat tube angle is 73º, head tube angle is also 73º

(we didn't do trig at my schools)

[T42]

The yardstick I'd use would be the rim diameter: it's standard and it's a good length, which makes scaling from it more reliable. "622 mm is the bead seat diameter, to get rim and tire companies compatible" quoth bikeforums.net.

[Kim]

The yardstick I'd use would be the rim diameter: it's standard and it's a good length, which makes scaling from it more reliable. "622 mm is the bead seat diameter, to get rim and tire companies compatible" quoth bikeforums.net.

Incidentally, the timing software we use for BHPC races allows us to measure the speed of bikes crossing the finish line by marking the rim diameter on a couple of frames of video.  Unfortunately the 622mm is hard-coded, which makes it mostly useless for HPV racing.

[slope]

Because I is a bit twp with ridiculously complicated programmes like Affinity Photo and after a couple of hours today not finding out how draw a line and determine its length (Photoshop definitely did do that with its 'Measure Tool'), I just printed off the photo and used a proper ruler = simples!

It turns out that this photo -

https://www.boardmanbikes.com/Assets/User/20215-BI_HYB_8.9_Electric_Bike.jpg

Is of a M frame and not only that, the saddle is within a couple of mm of my saddle height - so yeah yippee, the handlebars are as near as damn it level with the saddle height

This could be a spendy revelation . . .