Ebner: 
we are not so much interested in the absolute 
position or the absolute attitudes of cameras, 
but in relative positions. So that means the 
angles of rotation from one position to another. 
In  fact,: actually what you want. is to introduce 
these quantities to stabilize the geometry of the 
block rather than to solve to datum problem. These 
are two things which can be separated. At the 
rest of the networks you have tried to solve it by 
means of choosing a local datum for your coordinate 
computation, so I mean S-transformations. I think 
that we should look how a local datum could be 
defined or how we can define for these observations 
the form elements. 
Thank you. Are there any other questions? 
Torlegárd (Sweden): These studies are based on just simulations 
  
Ebner: 
Ackermann (FRG): 
  
and you have made a theoretical investigation of the 
resulting accuracy if you introduce these types of 
information in the system. My question is more 
related to the practical performance of photo 
flights. Do you have instruments onboard airplanes 
to record position data and attitude data? How 
far is it before we have those kinds of flights 
and what type of investment would be needed to put 
the instruments in the airplane, and are there 
systems that can prove data with a kind of accuracy 
you have assumed in your investigation? 
Thank you. Do you want to answer? 
It should be clear that this is a preliminary study 
only and the purpose of it is simply to show what 
results possibly to expect. Similar investigations 
have been done in aerial triangulation 20 years ago 
concerning the expected accuracy of block adjust- 
ment. The simple error models turned out later to 
give more realistic results than theoretically 
could have been expected. I do believe, therefore, 
although the objections against these simplified 
investigations are valid, that the results never- 
theless give an idea of what to expect. Later 
consideration of shift parameters and correlation 
may alter the results, but they are not expected 
to change the accuracy predictions fundamentally. 
The hardware situation is, however, something 
else. I have no clear overview about what equipment 
the companies are preparing. Certainly several 
companies have or prepare GPS receivers for use in 
airplanes. In Stuttgart, the institute for navi- 
gation also developes GPS receivers for high 
precision applications in airplanes or vehicles. 
We are expecting later this year the first test 
flight with prototypes of these receivers. In the 
beginning only pseudo range measurements will be 
possible. But next year the highly precise phase 
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