In Piranesi’s plan, the scale at the bottom of the sheet is divided in 6 segments. Consequently I assumed the scale went from 0 to 6 Roman Palms.
I chose meters as my default unit in the 3DMax environment. Then I draw a box as long as the Roman Palm’s scale in Piranesi’s imported plan. It measured 3.296 meters.
Then I built another box, measuring 6 IRF. Being an IRF = 0.2964 meters, my box measured 1.7784 mt
Finally, I calculate what percentage the scale on the Piranesi’s plan was of my known, hypothetical scale (53.95631%) and applied (through the scale tool in 3D Max) the same percentage of scaling to the entire plan.
After this operation, all the dimensions of the elements in my file where expressed in meters and easily measurable.
I repeated the same operation with the frontal elevation. The scale Piranesi used this time was 20 roman palm. So I calculate what is equivalent in meters of 20 IRF and tried to rescale the drawings. Theoretically, the two drawings, once rescaled according to IRF and translated in meters, were supposed to have consistent dimensions. I was surprised to see that the front elevation was much bigger than the plan and couldn’t possibly fit.
The reason was very simple. The 6 segments on the main plan stood for 60 and not 6 palms. I rescaled the first plan in 3D Max ten times its dimension (1000%). After this adjustment, the two drawings fitted quite well. This consistency allowed me to use the front elevation to derive the heights of some elements such as the core components of the temple and the four altars (two for side).