236 
PHOTOGRAM MET RIC ENGINEERING 
The general procedure of matching will be 
described in geometric terms. The left photo 
is considered to be divided into square areas, 
and each square, in turn, is considered in an 
attempt to find a matching area in the right 
photo. All of the squares forming a horizontal 
(parallel to .v-axis) band are considered before 
/Considering squares in another band. The 
second and third stages of matching are simi 
lar in operation to the first stage. 
There is enough room in the computer 
memory to store the parallax approximations 
for parts (B) and (C). The parallax approxi 
mations found by part (D), with interpola 
tion where necessary, are written on a tape as 
each band or strip of the left photo is matched. 
Each parallax difference on the output tape 
corresponds to a 6X6 spot area of the full- 
resolution left photo. 
Ortho-correction and Contour Program 
An orthophoto map with contours is pro 
duced after the correlation process. It repre 
sents an orthogonal view of the ground in 
which each object appears as though it is 
viewed from vertically above. Image dis 
placement caused by relief is one of the more 
significant errors in a real photograph result 
ing from the perspective view of camera-lens 
combination. The orthocorrection program 
corrects for image displacement resulting 
from relief and, in conjunction with the 
W ILD reproducer unit, generates an ortho 
photo map and/or a contour overlay. 
The 6X6 photo spot increment (15-mil 
square) on the left rectified photo tape is 
moved to its orthographic location on the 
basis of its elevation relative to the nadir- 
point. (»roups of six scans of rectified data are 
transferred into an input buffer where the 
elevation of each 6X6 spot area is computed 
from its associated parallax, previously de 
rived from the correlation phase and stored 
on a parallax tape. Each 6X6 spot area is 
assigned an elevation which, in conjunction 
with a series of algorithms, places a contour 
marker in each area whenever the elevation 
moves to the next higher or lower contour 
level. The contour placement algorithm 
verifies that each contour line is continuous 
and closes upon itself. After a correction fac 
tor is applied to the coordinates of each ele 
mental area, the data are shifted from the 
input buffer to its new' or ortho-corrected 
location until it is written on tape. The format 
of the output tape contains the ortho-cor 
rected photographic data in the low-order 
Maximum of density 
difference function is 
assigned to point P 
(x,y). 
N x M area in which point to be 
y “* M correlated lies, P x,y. 
h(l)* 
h(0).^ 
/1 
N 
i 
h(2) 
h(3) 
• 
h(4) 
\ 
Known elevation h(2) of the second of the 
four previously correlated points used to 
predict h (0). 
Fig. 12. Predicting parallax of P(x, y). 
bits of a character, with the contour spot 
markers appearing in the high-order bit. 
The present format for recording contour 
information on an overlay is as follows: 
1. Every fifth contour interval receives a 
darker shade of gray that makes it more 
discernible than the other contours. 
2. Each contour line is represented by a 
unique symbol to differentiate it from 
the adjoining contours. Five different 
symbols are available. A contour line is 
generated by interconnecting a series of 
6X6 spot areas in which the photo 
graphic detail has been replaced by an 
appropriate symbol. 
These marks are placed at each point where 
the parallax difference changes to a new con 
tour interval, producing a contour map in 
digital form. 
Tic Mark Program 
Planimetric maps usually contain identify 
ing information that shows the position of the 
photographs relative to some ground co 
ordinate system. The Tic Mark program 
inserts markers at 1,000-meter latitude and 
longitude intersections on the orthophoto or 
contour map. Based upon ground-control 
information and flight angle, an imaginary 
grid system is constructed to the scale of the 
map and oriented in a north-south direction. 
Those photo locations that coincide with a 
grid intersection are marked so that they can 
be identified on the final contour map. 
DAMC PREDICTIVE SYSTEM 
The major operational parts of the predic 
tive system are essentially completed (Figure 
10). The scope of this effort was to develop 
and show feasibility for a second experi 
mental programming system, and thereby to 
increase the system flexibility by providing