[WWI] drawing 3-views from photos

[Chris Banyai-Riepl]

Another issue that needs to be addressed is with the equipment that took the
photo.  A wide angle lens will introduce distortion, and a telephoto will
introduce compression.  This is obvious with very wide angle lenses and very
long telephoto lenses, so it is easy to see there.  But with ones that are
not obviously wide or tele, you will end up with increasing margins of
error, which can quickly ruin any attempts at making drawings.  Even with a
normal lens (say, 50mm), there can be parallax issues that also distort
attempts to measure precisely from a drawing.

If you have a long list of known measurements, then it can become easier, as
you can at least minimize the distortion factor.  For instance, if there is
an unknown object on your subject that you'd like to draw up, say a new type
of bomb, and you have measurements of the guns, fuselage height, propeller
diameter, etc., you can measure the knowns in the photo and establish a
ratio of actual/photo dimensions and use that to get a set of close
dimensions of the unknown object.  Of course, the more dimensions you know,
the more accurate the interpolation will be, and the more mathematical can
even use this to plot distortion curves for wide angle lenses and get more
precise measurements from those images.  I did that once, and it required
quite a few known measurements to get a decent function set.

Sincerely,
Chris Banyai-Riepl
Publisher
Internet Modeler
http://www.internetmodeler.com