AUTOMATIC PHOTOGRAMMETRIC INSTRUMENTS 
13 
Fig. 9. Photodigitizing unit of the digital automatic map compilation system. 
Compilation System has been extensively re 
ported to the American Society of Photo- 
grammetry. It consists of a photodigitizing 
unit for scanning and digitizing the overlap 
portion of stereo diapositives, specially 
written computer programs for use on an 
IBM 7090 Computer to perform rectification, 
correlation and ortho-correction on the digital 
photographic data, and a photomap printing 
unit for printing the orthophotomap with 
contours and grid tic information. Unlike 
UAMCE these operations of scanning, cor 
relating and printing are performed see 
quentially; each being completed before the 
next is initiated. Also, it should be noted that 
all of the data processing is done with the 
terrain data in digital form; i.e., the photo 
rectification and the image correlation. 
The photodigitizer consists of a CBS line- 
scan tube mounted on a Wild STK-1 Stereo 
comparator. This assembly is shown in 
Figure 9. By use of a split optical system, each 
stereopair is scanned simultaneously in the 
line-scan tube and the photographic density 
of each element recorded on magnetic tape as 
a function of its position. In the present sys 
tem, eight shades of gray are used. From the 
orientation of each photograph, the digital 
record of the photograph is corrected or “rec 
tified” in the computer to produce a digital 
tape record of the equivalent vertical photo 
graph. The tape records of the rectified 
stereopairs are now correlated in the com 
puter to determine relative “parallax be 
tween conjugate images” or AT-shift between 
sequences of digits in the records. Establish 
ing the parallax for a point determines the 
shift to be made to form an orthophotograph, 
as well as the elevation data for contours. 
After the data processing in the computer, 
the orthophotograph in magnetic tape form 
with contour and grid tic data superimposed 
can be redirected through the STK-1 and 
line-scan tube to produce a photographic 
record in eight shades of gray. 
Digital mapping has the potential of great 
versatility; since, as is the case with the 
analytical plotter and the UAMCE, the 
geometry of the sensed data presents no real 
limitation to its use with the system. More 
over, digital techniques also show real promise 
in the cartographic area as Mr. Sharp dis 
cusses in his paper, “Impact of Data Proc 
essing on Photogrammetric Instrumenta 
tion,” Invited Paper No. 11 -5 for the Lisbon 
Congress. 
There are two major problems in digital 
mapping which are receiving considerable 
attention, scanning and correlation. Although 
presently employing the line-scan tubes, 
IBM has developed in this application, a 
drum scanner/printer for use in digital 
cartographic systems. This unit scans and 
digitizes in 16 shades of gray, photographs at