I just completed the survey before reading the thread and my feeling was pretty much the same as most other posters here. I think I used my experience of flight simulator flying more than actual flying experience to guess the altitude from which everything else was based. Ground texture is the only thing you can really use for altitude when you don't have an altimeter. In fact you can use the cloud base as well once you have confirmed its height (not a good idea really).
It did raise the question though about how accurately I could guess the altitude with real imagery. At low levels it's fairly easy, but looking at video stills from 2000 feet and up (where I know the altitude), I could just as easily guess it wrong.
Last edited by The500man; 26th Feb 2013 at 12:48.