The highest accuracy verticality information can be obtained either by inexpensive good-quality 
horizon photography (if practicable under the given circumstances), or by the highest degree of 
precision in inertial system component parts, which requires high investment. **) 
With all technological know-how of this space navigation age, there seems to be an asymptotic 
limit - at least for the near future - at the 1' or 2 C level. 
IV. 3 Integrated systems. 
System components are available as building blocks for integrated measurement and guidance 
systems of great capability; thereby, these systems become also systems of great investment 
problems. Economically, their justification is doubtful but non-photogrammetric considerations 
as well as the time factor may be more decisive than cost. 
IV. 4 Outlook. 
One of the challenges of the near future may be to find the optimum task division between 
photogrammetric methods and flight-functional possibilities: they should be matched to the 
optimum solution of aerial survey problems. 
**) This is valid for the inertial platform as such, irrespective of whether its output is used 
to be recorded only, or also to control aircraft heading or camera axis verticality.