Georgia Coordinate Mapping Committee. A major responsibility of DOT was 
to spot check the accuracies of the photogrammetric results by means of 
independent ground surveys. The project encompassed a 3x4 mile area as 
shown in Figure 7. At nominal half mile intervals within this area 
potential locations for permanent monuments were selected — a total of 
63 locations in all. Actual locations of monuments were established by 
field reconnaissance to be as close as possible to the ideal locations 
laid out on a map. As can be seen from Figure 7 which depicts the actual 
locations of the monuments, it turned out to be possible to adhere rather 
closely to the planned layout despite the wooded, hilly and built-up 
character of the landscape. Near each of the selected locations of the 
monuments two circular targets of 32 inch diameter were painted in 
fluorescent arange along the center of the adjacent roadway. The separation 
of the targets was preset to be precisely 30 feet and the center of each 
target was marked by a surveyor's nail. The monument itself, whether 
actual or potential (some were put in after the photography), was located 
off the roadway along the nominal perpendicular bisector of the line join- 
ing the two painted targets as shown in Figure 8. In those cases where 
monuments were actually implanted, the offset distances of the monument 
from the centers of the two painted targets were measured along with the 
differences in height between the monument and the centers of the targets. 
From these easily made offset measurements and the coordinates (ultimately 
to be established photogrammetrically) of the neighboring targets it becomes 
a simple matter to compute the precise coordinates of the monument itself. 
This means that the permanent monument need not actually be installed prior 
to the photography — it can be installed at any desired later time as long 
as the centers of the associated offset targets remain recoverable. This 
constitutes a significant advantage of the offset target method, for the 
installation of monuments is a far more time consuming and tedious task 
than the painting of dual targets in the roadway. Moreover, because of 
the designed proximity of each eventual monument to corresponding pairs of 
painted monuments, the necessary offset measurements can be made quickly, 
easily and inexpensively by relatively unskilled personnel. Two other 
advantages of this approach are noteworthy: vandalism of movable targets 
placed over monuments is a major problem in urban areas, whereas targets 
painted in the roadway are virtually immune to disruption; and such 
targets are less likely than the monument itself to be obscured in the 
photography by nearby trees or structures. 
In addition to the 63 pairs of offset targets just discussed, 
.a total of 32 painted, single targets was established close to the 
boundary of the block to serve as wing pass points to help strengthen ı 
the photogrammetric adjustment. Horizontal control was provided by six 
paneled, first order points indicated in Figure 7. With the exception 
of the station Pershing vertical control coincided with horizontal 
control. In addition to this vertical control, a single vertical point 
(DOT 32) was especially established near the center of the block by the 
Georgia DOT. 
Photographic coverage of the test area was taken at a scale of 
1 : 17,500 (altitude ~ 4900 ft) with DBA's Zeiss RMKA 8.5/23 camera using, 
as in Vermont, the DBA 61 point reseau platen. With both forward and side 
overlap of 60%, each photo contained a rather uniform pattern of 25 points 
(or pairs of points). The photographs proved to be of excellent quality. 
Moreover, none of the painted targets was obscured. This demonstrated 
that near optimal distribution of targets is altogether practical in an 
urban area even when photography is performed with a super wide angle 
camera and thus answered one of the questions raised before the test. 
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