05-03-2013, 04:44 PM
I'm not sure about 1, i tend to guesstimate with measurements, if it looks roughly right then i go with it. I'm sure someone else will be able to say precisely. As to 2, if you're drawing something that is not inline with the perspective grid you;ve set up...you draw (or visualise) a new vanishing point or points for this new object, along the same horizon line (if its on the same plane), but cross reference the original perspective grid to see if it falls in line with it, again you;re kind of eyeballing it for the measurement. I'd be interested to see a more specific approach to doing this too, if anyone else knows?