"If you are measuring against other objects, use the orthogonal cameras, as they do not exhibit perspective..."

That's not necessary if you build yourself a "metering cube".

You simply scale the cube to the dimensions you want, then scale the prop or figure until it's covered by the cube.

In this example, a full scale Lancaster Bomber was shrunken into a 1/72nd scale model of a Lancaster.

The original had a wingspan of 31.09 meters, so the model needs to have a span of 43.1 cm.

And the best thing is you can measure all three dimensions simultanously.