Fig. 5. The base triangle which supported the cameras. Note the spirit levels for 
the check of the horizontation. 
In Table 2 the coordinates and elevations of the control points for the 
oblique photography according to the measurements in 1957 are demon- 
strated. 
The control points were signalled during the photography with cir- 
cular metal disks, diameter — 120 mm, which could be placed upon the 
iron tubes with the aid of well fitting plugs. The center of the signals 
were marked with a white circular surface, diameter — 40 mm. Then 
followed a black circle ring 25 mm and finally a white ring 15 mm, see 
Fig. 3. 
On the ground a number of full contrast resolving power targets 
were placed, Fig. 4. The purpose of these targets was primarily to regis- 
ter differences in the resolving power from one camera and exposure 
to another. 
2.2. The camera installation 
With three theodolites a point was determined in the tower, verti- 
cally above the center point 0. The point in the tower was marked with 
11