P3D Re: Aerial 3d !

[Bob Wier <wier@xxxxxxxxxxxxxxxxx>]

At 2:16 PM -0700 on 2/9/98, John Gaasland wrote:


|Met a person in the building I work in today. He works in the
|photogrametry section with 3d-photos taken from planes. There is a

Yes - back when I was an undergrad taking civil engineering classes
(before computers were invented :-) I spent some time using a Kelsh
(sp? I forget) plotter. The way you used to plot countour maps was
that you'd have two photos (usually glass plates for dimensional
stability) operating as transparencies, shining down on the table.
You'd look thru the viewer at them and would "fly" around with a pivot
arm, moving it up and down to match the level of the ground to indicate
the height above a given baseline. 

One of the first programs I ever wrote (on an IBM 1620) was to do
rectification of ground control points to bring the orientation of
the plotter table into conformance with what was actually being
seen thru the viewer. This was via Fortran II...you had a bunch
of variables to swamp out such as the camera in the airplane not
being perfectly perpendicular to the ground, and also it crabbing
sideways along the line of flight due to crosswinds...

I had a humerous experience one time doing a lab using a transit - 
a group of 4 guys were to run a traverse around the campus library 
starting from a fireplug. To get credit for the lab, your measurements
on forward and backward sights had to match to within some precision -
I forget what - maybe an inch in 1/4 mile. 

The hook to the story is that there was construction going on at the
time, and when we were around out of sight on the far side of the 
library, a bulldozer came along and HIT the fireplug, causing it to
slant at rather a pronounced angle - so we were off both vertically
AND horizontally. 

The guy teaching the class laughed and laughed...

               Bob Wier
         mailto:wier@xxxxxxxxxxxxxxxxx
    10:23 PM Monday, February 9, 1998
     Rocky Mountain College, Billings MT.
 keeper of the Photo-3d and Overland-Trails
mailing lists and the USA GPS Waypoint server 
 



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