A (preferably) flat test field, containing a great number 
of regularly around the center-point located, signalized 
points (e.g. a grid) is photographed from a point on the 
perpendicular through the center point of the field and 
with the negative plane approximately parallel to the 
test field. The relative location of the points of the test 
field shall preferably be known with such a high quality, 
that the errors of the coordinates, reduced to the scale of 
the negative can be neglected in comparison with other 
errors of the image coordinates. Next, some examples of 
such test fields, used in the present work, will be briefly 
described. 
For aerial photographs 
The Oland test field (6x6 kilometers), containing 162 
test points, well signalized and marked in a nearly flat bed 
rock area, Ref. 3:1. The standard errors of the coordinates 
do not exceed 20 mm. 1 The field has been used for a great 
number of partial calibrations of aerial photographs from 
many cameras. 
For terrestrial photographs 
a. A test field on an outer house wall (36 x 16 meters), 
containing 87 signalized points, Fig. 3:1. The standard 
errors of the coordinates have been estimated to be less 
than 1 mm. The distance is 26.172 m. 
b. A test field on an inside wall (5x3.6 meters), con 
taining 45 signalized points, Fig. 3: 2. The standard errors 
of the coordinates have been estimated to be less than 0.1 
mm. Two exposure stations (distances 2.761 and 6.900 m) 
are located on the normal from the center point. 
c. A test field located on a cast iron plate (1.4 x 1.0 
meters), containing 119 signalized points, Fig. 3:3. The 
standard errors of the coordinates have been estimated to 
be less than 0.02 mm. 
d. A negative glass grid (24x24 cm), contact print of 
the grid Wild No. 410, containing 576 points of intersection 
of grid lines. In Fig. 3: 4 the grid is in use. 
e. A glass grid (24x36 mm) with mm-spacing. In Fig. 
3: 5 the grid is in use. 
f. A glass grid (2x2 mm) with 0.05 mm spacing for 
test of microscopes, etc. 
g. A set of lead plates on a plexiglass plate (24 x 24 cm) 
for tests of X-ray instruments. In the lead plates small 
holes are drilled, defining the points. 
The coordinates of all devices d through g are deter 
mined with the stereocomparator Wild StK 824. The 
standard errors of the coordinates are therefore of the 
order of magnitude 1 micrometer (micron). 
It should be noted that the radial distortion effects of 
photographs have been determined by two methods: 
1. From the scale variation of circular combinations of 
test points around the center point. Each circle combina 
tion is adjusted separately. 
2. From a fifth order polynomial. In this case the image 
coordinates have usually been given equal weights. 
The two methods have frequently been used simul 
taneously for comparison. 
Particular attention has been paid to the determination 
of radial distortion effects in photographs (and projectors) 
because of the possibility of correcting such distortion 
effects with various devices. 
1 This accuracy information refers to the adjustment of the 
geodetic measurements, performed by the Geographical Survey 
Office.