5 07 189 
XIII Congress of the 
International Society for Photogrammetry 
Helsinki, 1976 
Commission V 
Working Group V/2 
Invited Paper 
OTTO R. KöLBL 
Swiss Forest Research Institut 
Birmensdorf (ZH), Switzerland 
Metric or Non-Metric Cameras 
Non-metric cameras may be sufficiently accurate if narrow 
cone angles, and analytical methods 
are employed. 
(Abstracts on next page) 
INTRODUCTION 
ARIOUS PROBLEMS in engineering require 
high precision measurements. In many 
cases photogrammetric methods have 
proved to be extremely useful. Special ad- 
vantages of this measuring technique are its 
high precision and great versatility; further- 
more, the object itself is not touched by the 
measuring tool. 
Special cameras (mono- and stereo- 
cameras) and measuring devices (Wild A-40, 
Zeiss Terragraph, and others) have been 
developed to take and restitute the photo- 
graphs. These instruments are conceived for 
the production of plans, profiles, or contour 
maps and demand very few numerical com- 
putations. The restitution instruments can be 
considered as analog computers and are con- 
structed for specific camera arrangements. 
These limitations simplify considerably the 
handling of the equipment and permit an 
efficient operation. In general only photo- 
graphs with parallel camera axes can be used 
(e.g., Zeiss Terragraph) and consequently 
the base-to-height ratio and the accuracy in 
depth is very limited. 
The standard outputs of analog restitution 
instruments are in a graphical form. Besides 
the graphical representation of the measure- 
ments, digital methods are increasingly used 
for the description of an object. The data are 
very flexible and suitable for further process- 
ing with electronic computers. Although au- 
tomatic coordinate registration devices can 
be connected to analog plotters, it is advisa- 
PHOTOGRAMMETRIC ENGINEERING AND REMOTE SENSING, 
Vol. 42, No. 1, January 1976, pp. 103-113. 
ble to use mono- or stereocomparators for the 
measurements. Comparators offer a higher 
measuring accuracy than the analog plotters, 
and furthermore there are practically no limi- 
tations for the camera arrangement. Devia- 
tions from the normal case of photogram- 
metry do not cause any time delay in the 
restitution phase, as the orientation of the 
stereo model is achieved analytically by the 
computer. Consequently, convergent photo- 
graphs can be used without restrictions, and 
systematic errors of the picture coordinates 
caused by lens distortion, film shrinkage, etc. 
can be taken into account. 
Under these conditions photogrammetric 
measurements are no longer restricted to 
pictures taken with metric cameras. This is of 
great importance because for many applica- 
tions appropriate cameras are not available, 
such as in close-range photogrammetry for 
distances of less than 2 meters. The optical 
industry has also developed several highly 
specialized cameras for various applications 
which can be used for metric applications as 
well. Then photogrammetric measuring 
techniques are not bound to specific survey- 
ing instruments, which might give impetus 
to a wider application of these methods.! 
In this paper the accuracy limitations 
which are caused by the properties of non- 
metric cameras are discussed and the differ- 
ences in application of metric and non-metric 
cameras are pointed out. In the beginning a 
definition is given for the term "metric 
cameras", and accuracy tolerances for the 
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