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1. INTRODUCTION 
The investigations of the Working Group on Image Geometry during 
the last four years centered on two photogrammetric cameras with wide 
angle lenses and a precision réseau. Whereas the bulk of investiga- 
tions aimed at camera calibrations of the laboratory type, there have 
only been two reports on calibrations under real working conditions 
(e.g. Kupfer 1976 aj;Merchant 1975). The first group should evaluate 
the inner orientation of the cameras under very close describable con- 
ditions, which ensures a high degree of repeatability of calibration 
results. Furthermore the real laboratory calibrations from different 
investigators should be in good agreement with each other. À certain 
check of this assumption is given elsewhere (Merchant 1977). The dis- 
crepancies showing up in this check are among others at least an addi- 
tional proof of the limitations of laboratory calibrations, applied to e 
photogrammetric tasks, expecially analytical precision photogrammetry. 
Hence one needs not appraise system calibration as a remedy in 
its today's most common manner, i.e. field calibration, using test 
areas, or "self calibration" using informations given by the imagery 
from the survey flight under consideration. This paper deals, accor- 
ding to the aims of this Working Group, mainly with the first mentioned 
type. 
The shortcomings of field calibrations of photogrammetric systems 
are as well known as are their advantages. A full system calibration 
may only be reached in geodetically well surveyed specially chosen 
mountain areas. Merchant's "Mixed Ranges" are a well acceptable compro- 
mise (Merchant 1975). 
However ''the usual aerial photo case" is that "all targeted object 
space points tend to lie in a common plane' (quoted from the paper 
just mentioned). Hence a nearly level test area with sufficient supply e 
of well defined object points and control sure enough may give satis- 
factory results in partial system calibration for just this every day 
case of photogrammetry with a minimum of effort. The limitations of 
this procedure, i.e. allowing for deviations from level terrain and 
normal case of aerial photography have still to be investigated more 
closely. On the other hand the effectiveness of the procedure has been 
proven to a satisfacting extent (e.g. Kupfer 1975, Kupfer 1978). 
It should be stressed with some accentuation (which has been done 
several times by now) that a test area with sufficient control and 
targeted points could be quite temporary and geographically part of a 
mission area, depending on circumstances. The show-down of field cali- 
bration versus "self calibration" is not yet finished. Typical short- 
comings of the latter are, e.g. dependence upon sufficient control, 
regular pattern of image points, absence of gross errors etc. These 
shortcomings increase with the decrease of real observations.