The thickness of things

Before deciding which plan I will have used as main starting point for my modelling, I wanted to check their consistency. I created a file with Adobe Photoshop and, after reducing the opacity of the three plans (Saint-Non's, Piranesi's, Soane's) I put each one on top of the other.

I have chosen one single element to compare the three plans (the right side of the colonnade, watching the Temple from the front) and rescaled them in Photoshop until that element was the same in all the three layers. 

LEFT: Piranesi and Soane's plans RIGHT: Saint-Non and Soane's plans

This superimposition has showed that none of the maps is a perfect match with any other. 

However, Piranesi’s map and Soane’s one have a certain degree of consistency while Saint-non’s map appears to be remarkably different from both of the other two.

I believe this discrepancy does not disqualify any of sources. These kind of differences can be due to many variables including the thickness of the pencil, the texture of the paper, human error in measuring, transcribing or drawings or simply the very difficult task of taking measures of such an irregular and massive building as a partly damaged Roman temple.
Moreover, working not with the originals but with digital copies, we have to take into account an other potential level of data corruption.