Just for sharing/education I thought I would describe how I usually find the scales of things from photos, which I do a lot for my sculptures.

Here’s one wall of the map room in the NY Public Library, I already know it’s 34 feet wide because I found that fact in an article, so I would first look around for something of known size, if an adult person is standing there you can use a rounded out 6 feet for the scale, in this case the only known size is the width of the room.

Now I want to find out the size of the corbels in that cornice or entablature at the top of the wall, but notice the round top pseudo window in the center means that cornice is broken and there are none across that space to count, so I made a red box across 6 adjacent corbels, briefly moved it over to the pseudo window and could tell that space would have had 6 corbels across it.

I counted 9 corbels on each side, plus the 6 comes to 24 total spanning 34 feet, 34 ft x 12 inches = 408 inches, divided by 24 corbels means each is spaced 17-1/2 inches center to center, now we’re cooking because we have a measurement to use for all the rest:

Now I imported a cropped, lightened up and slightly desaturated to reduce the shin of the gold- enlarged version of the picture into CAD software, and after scaling the picture properly using that 17-1/2″ measurement I was able to begin making measurements of landmarks to start with:

The good thing is the original picture was taken pretty straight-on, and with a minimum of paralax angles caused by taking a photo looking up at something tall, there is a little here because of the height of the ceiling, but one can get reasonably close enough measurements with this that using a little fudging will get it accurate enough for this use.

If I lacked the room width to begin with, that EXIT sign and that wall clock would be the second choice for scaling off in CAD, because those exit signs are a pretty standard size and can be determined with a search, the wall clock too but it’s a little less likely to be any standard size, but most of them around this size would be around 16″ across- it would be my last choice to scale from if I have other choices.

We see the wood cornice with the corbels is 3 feet 3″ high, the coffers in the photo due to the angle of view give us the illusion they have height we can measure just like the cornice- they do have heigh, but if we were to measure that coffer from this photo going from the top of the dark cornice up it would be wrong due to the angle- the measurement that way is actually from the projection of the cornice’s edge towards you at the camera which is measuring the room length not the coffer’s depth- thats the optical illusion one has to be careful of when scaling off photos!

I was able to extract 4 more measurements above the coffers and if one looks carefully there is another optical illusion between the two 6-1/2″ measurements because that section of the ceiling projects horizontally towards the camera just like the coffers are.

The top measurement of 1 foot 11 inches is another major molding, a concave repeating molding with beed and fluting designs, it sits on top of a 6-1/” tall egg & dart molding, the other 6-1/2″ molding is a Greek styled leaf design.

We also can see the green painted wall is 7 feet 1 inch from the wainscot to the cornice bottom, the pseudo window is 8 feet wide, and the shield over it is 2 foot 9-1/2″ wide.

So in just a few minutes we have the majority of the measurements needed, the rest can be found with other photos, and whatever is missing can be guessed at with reasonable accuracy.

This photo would provide the square coffer’s width, we can assume that one IS square and determine it’s other measurement front to back, the one to the left of it would be the same front to back, it’s width can also be found in this photo and it’s rounded corner approximated easily although very hard to see here- there is a quarter round DOME above the pseudo window and that shield is not directly over that pseudo window as it appears- another optical illusion- it’s actually several feet closer to the camera, this also tends to make the measurement of that ( 2 foot 9-1/2″ ) a little incorrect because it is closer to the camera/viewer than the wall where the cornice is, but the camera is far enough away the error is really minimal here.

I also discovered when I lightened up another photo of that cornice- between each corbel there is a lion’s head carving, and each one is holding the end of a swag which curves along the bottom of each corbel which can be seen in the above photo.

So that is the method I came up with years ago.