Finland 
3 
now the ratio has been calculated using a known point distance or a scale check line and 
a »rectifying key». Here the same is determined by the rectifying level (the ground level on 
which the picture, according to known points of vertical control, is to be rectified) and the 
corresponding flying heights given by the statoscope readings. 
For that purpose a proper base level (H 0 ) for the ground to be mapped is choosen 
and the base enlarging ratio (j 0 ) is calculated for every ioth or 15th picture of 
the flight using known point distances, their heights, statoscope readings and angles of tilt. 
This figure s 0 shows the enlarging ratio to be used in the rectifier in order to get a proper 
scale for the ground level H a when the statoscope reading of the picture is = o (flying height h 0 ). 
In the practice it has appeared that the base ratios (l 0 ) obtained for pictures of the same 
flight generally deviate from their mean value only 1 to 2 °/ 00 even when the flight has lasted 
some hours. 
Using the mean value of the base ratio (s 0 ) the enlarging ratio for each picture is calculated 
according to the corresponding statoscope reading (a h n ) and rectifying level as follows 
This fast and simple method has given very satisfactory results in compilation of controlled 
mosaics in scales 1 : 4 000, 1:10 000 and 1 : 20 000. 
In J 955 a t es t survey of an Aviogon-camera RC 5a was accomplished. An archipelago- 
area was photographed at a flight altitude of 2 300 metres on both film and plates, and seven 
pairs of film and plate negatives were tested in a Wild A 8 in order to determine the possible 
systematic error in elevation caused by the lens distortion and other possible error sources. 
In A 8 a close net of spot elevations was measured on the shore lines and »contour lines» were 
drawn. All models gave the same systematic swelling on the center of the model. The same 
result was later obtained also from other pictures with plenty of predetermined spot eleva 
tions. According to the test results an elevation error figure was drawn, which casually has 
been used in levelling of models when the spot elevations were scattered unevenly on the 
model area. 
Education. 
In Finland the photogrammetric education is given at the Institute of Technology and at 
the War College. Provisory courses in photogrammetry are also occasionally given e.g. once 
a year. A chair in photogrammetry is proposed to be founded at the Institute of Technology 
in Helsinki. 
The Society. 
The Finnish Society of Photogrammetry was founded in the year 1931, and was accepted 
as a member of the International Society of photogrammetry in 1934. The membership of 
our society has increased steadily comprising now about 100 members. 
Our society has not had means to publish regular journals, but two special publications 
have been published, the first in 1946 and the second in 1954. Separate prints of papers, 
published in other periodicals, have often been distributed among the members. 
President of the society is now Mr K. Lofstrom, Engineer-Lieutenant-Colonel and 
Secretary Mr M. Tikka, M.Sc.