Model Forum / General / Models / November 2007

Albert <albertcherer@comcast.net> wrote in news:1194662504.649578.200610
@v2g2000hsf.googlegroups.com:

I recall a computer program that was developed for making 3-view drawings
using scans of articles - I had a demo of it somewhere, once. If I can
find it, I'll post the name here and let you know. But don't hold your
breath.

RobG
(The Aussie one)

That IS indeed a tough one.  When I am taking my own pictures, I can
ensure that I am perpendicular to major axes.

However, on some subjects I am left with only quartering pictures.  If
one were to use pure photogrammetry, one needs to know the distance
from the subject to the camera as well as the camera lens focal
length, not very practical unless you know the photographer.

Therefore, you can only deal with relative distances.  You need some
basic dimensions that you will NOT be able to obtain from the photos.

Vertical dimensions are the easiest ones to scale, since most
prototypes are shorter in that direction than in other directions.
You assume that everything in a vertical column is indeed vertical and
so is the same distance from camera (assuming camera is held
reasonably level).  Now you can measure distances along that vertical
and ratio the sizes.  This does only give you relative dimensions,
which is why you need some basic dimensions.

While many photo editing programs these days have a perspective
correction function, this is certainly imperfect for any direction
with a component along the camera line of sight.

BTW, I taught myself to use CAD when I was trying to make scale
drawings from a number of photographs of a race car.  Fortunately, I
did know the wheelbase and width of the car, and the tire sizes.  I
used what I learned from that exercise to take or seek out photographs
of many vintage race cars, which I did five-views of, and I do sell a
CD-ROM of scale drawings and photos for vintage oval track race cars.