Re: mapmaking and stereo viewing, anecdote,

[wier@xxxxxxxxxxxxxxx (Bob Wier)]

>
>The fellows operating those machines, *THEY* had stereoacuity!!!
>
>pno

Kelsh Plotters they were called. There were also Wild autographs (with
the A8 being a favorite model), and Balplex.

I was trained on the use of one for
awhile (in a previous life). Generally you had two glass plate positives
(perhaps 8*10 in size early on - later smaller sizes were used). It
was fun to use it (well, as least *I* thought so). You had elevation
benchmarks on the ground established so you could see 'em (usually by
the field crews laying out paper/cloth X marks when the plane flew
over). If you had three of them visible, you could establish a plane.
It was a bit tricky since you had to correct for any roll, pitch or
yaw in the plane when the photos were taken. Once you rectified the
two photos, you could look thru the glasses (I guess they must have
been polarized, but I can't remember for sure) and "flew" a spot
of white light around the ground. You could adjust height of the 
target and it moved a little scale which in turn could be used 
to determine elevation of a point. Alternately, you could set
the target for a given calculated altitude and "trace around"
in 3-d space following the countours of the ground (producing
contour maps) using the tracing table platen.

Doing those rectification calculations was a bear. Slide rules and
mechanical calculators. One of the very first computer programs
I wrote (in Fortran II!) was to automate that.

Gee - hadn't thought about one of those for years.

THANKS

  -------- Bob Wier ----- wier@xxxxxxxxxxxxxxx -----
  East Texas State University Computer Science Dept.
   keeper of the Photo-3d, Motorola MC68HC11, ICOM
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