Table 1 
Data of the photographs used for the research work. 
Panchromatic Film. 
Camera: Wild RC 5a aviogon. Focal length 15 em (6” 
Negative size 2323. cm (9^). 
  
Time Picture Relative Base- 
of Quality Length of Height 
Photography 1—5 Shadows Ratio 
Flying Negative 
Ficld Altitude Scale 
  
Hällnäs 4.100 :96 900 21/8 13000'cl : 0.61 
4.900 :32 100 17/8 1001 » d : 0.49 
Ostad 2.515 :16 500. 4/6 0929 I ; 0.60 
! 040 :26 500 12/7 0913 : 0.56 
5.135 - 33700 4/6 1000 F ; 0.59 
V:a Skedvi 2.545 :16 100 30/5 0934 A 0.51 
3.955 :95 900 21/6 0939 » : : 0.56 
) 
5.160 : 33 800 21/6 0822 » : À 0.50 
Aerial photos used for maps. 
Originally the photos were used primarily for maps. The 
demand of accuracy in forestry maps is not greater, as a rule, 
than can be satisfied by the photo scale, upon which the Economic 
Map of Sweden is based. Therefore, it was not deemed necessary 
to deal with this problem in the investigations. 
1. 2. Aerial photos used for measurements. 
Hitherto measurements on aerial photos, for instance tree 
height determinations, elevation determinations ete., have been 
made to a very small extent for practical purposes. Still it 
has been considered of interest to establish the effect of photo 
scale on the accuracy of these measurements. The measure- 
ments here performed were confined to height determinations 
of single trees and stands. The measurements were made, pri- 
marily, by means of mirror stereoscopes and stereometers. 
A number of single trees were selected within the three tesl 
fields, Hàllnàs, V. Skedvi and Ostad (50—130 trees in each 
field). The tree heights were determined in the field by means 
of Blume-Leiss tree height measurer (hypsometer). The heights 
were approximated to the nearest half metre. The trees were 
indentified and marked in the photos. In each test field a 
J