I scaled off a large format B&W .tif image obtained from the Library of Congress’ historic American building survey to find the dimensions. The technique is easy with this photo since not only is it a straight-on shot with no distorsion, but I have one known measurement to use to calculate the scale of the objects in the photo with.
Using the ruler in an image editor I found the measurement of one of the medallions I own (not shown in the view) which is 18″ to come up with a pixel measurement of the section where the yellow line is. I found that yellow line compared to the size of the line for one of the medallions that was cropped out of this view makes it 470 px which came to 34,” so using those two values I came up with a divisor of 13.8 px per inch.
Now it’s simply a matter of taking pixel measurements and dividing by 13.8 to get inches, and then by 12 to get feet.
The pixel value and pixels per inch will of course change with every photo, it is not a constant number.
Using that method I found the white line is 23″ the blue line should have stopped above the street name to show that upper section’s measurement, but from the name to the yellow line is 48″ and the long blue line is 81.”
The long red line is 15 feet 6″ while the “wingspan” above which is not color lined is 11 feet 8,” so it should be obvious how massive this ironwork was.
The smaller winged piece on top the white and yellow line measure was made separately and it was 500#.
So to make a model of this, probably 36″ is going to be about the maximum width I’d want to go and would include everything in the photo, including the riveted railing which in this photo is 9 feet 4″ high.
That would mean a model scaled down to represent 16 feet of width, if it is 36″ wide (X,Y) then that scales to about 32″ high (Z) in CAD software rounded out to the nearest whole inch.
I’ll have to play around with the scaling to come up with the best size.