C51 77 
dx 
oo 
(68) 
- dxs5 
(69) 
- dxss 
(70) 
p d 
dxss 
(71) 
(72) 
(73) 
(74) 
(75) 
(76) 
(77) 
(78) 
(79) 
(80) 
(81) 
(82) 
  
  
Fig. 12. The Oland test field. The triangles indicate twenty-five trigonometric 
points located in the corners of a grid 6 X 6 km. The coordinates and elevations 
of the points are determined geodetically with very high accuracy. Standard errors 
of the individual coordinates are of the magnitude 20 mm. The points are per- 
manently marked in the rock and are signalled with circular concrete plates. 
The radial distortion is of particular interest. From the expression 
(59) the distortion can be determined from different circles as the va- 
riations of de. The corresponding analytical expressions are very 
simple. 
5. Some investigations of aerial photographs over the Oland test 
area 
The Oland test area has been photographed from the altitude 5000 
meters with different cameras. Here we will demonstrate the deter- 
mination of non-projective systematic errors, primarily radial distor- 
49