On the Vertical Accuracy of Aerial Photographs 
365 
By 
Taichi Oshima* 3 and Yoshihira Usami** 3 
1. Introduction 
Recently, there, have been many developments in instruments and methods 
used for making topographic maps by photogrammetry and the results are used 
not only for reconnaissince work, but also for all stages of planning to the final 
design through the use of large scale mapping. Photogrammetry is becoming a 
widely accepted method of mapping with many uses. Even so, photogrammetric 
techniques have their limitation because of conditions governing the flying height 
during photography and the operation of the plotting instruments concerned. Until 
now there have not been any publications directly investigating the accuracy of 
vertical aerical photogrammetry in this country. Those who use aerial photographs, 
sometimes ask how much reliance they can place on the aerial photographs from 
the point of the accuracy obtained by photogrammetry. Therefore, the authors 
carried out a test to show the relationship between flying height and the accuracy 
of photogrammetric measurements. This work covers a comparison of data obtained 
from direct levelling with photogrammetric measurements as a preliminary step. 
The tests were made using some of the plotting instruments which are now in 
use in this country. The main purpose of the tests concentrated on checking 
the differences in the degree of accuracy resulting from the operator’s experience, 
the plotting instrument and the accuracy of the plotting machine, both with and 
without on aviogon correction plate. 
2. The Test Site 
As the test site, a district in the south western part of Tokyo was selected 
as it was quiet and free from conjested traffic, and because direct levelling had 
already been carried out there. The checking points which were used to check 
the height accuracy were arranged in a network in the form of a grid system 
over the entire area photographed, as shown in photo. 1 and fig. 1. This area 
consists of continuous small hills about 10 metres in height. The checking points 
are shown as small circles on the photograph and numbered 1 to 69, and the points 
marked by a triangle were used for orientation in the plotting instrument. 
3. Photography and Height Measurement Procedures 
The photography was taken from a height of 1,211 m. using a R. C. 8 Camera 
with an Aviogon Lens (focal length f=152.82 mm). Accordingly, the photographic 
* } The Institute of Iudustrial Science, The University of Tokyo. 
** ) Pacific Aero Survey Company Ltd, 
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