I typically try to find a couple of measurements from a spec sheet, and then scale a photo or diagram as a canvas in fusion 360 to match the known sizes.
E.g. from the spec sheet of the CAT 390F excavator, I can see that the length from the center to the very back is X meters, and the height from the ground up to the counterweight is Y meters. I insert the canvas and then scale it to match the known measurements.
After the canvas has been scaled properly, I can draw on top of it to match the sizes:
Insert canvas:
Switch to orthograpic view:
Draw in the objects:
Switch back to perspective view:
Hide canvas:
Best regards,
Stein :-)