adjustment. Depending on the application area and the 
desired image scale the required positioning accuracy 
may vary significantly. The Figures 1 and 2 summarize 
the respective required accuracies for the two application 
areas. 
  
  
  
  
  
350 
300 
E 250 | 
D 
8 200 1 - 
= 
8 450 1 — 7 
© 
g 100 - 
50 4 
g | iz 
© © © © © © © 
e C) © ce e e e 
© wn © © e e e 
v CN LM © un c © 
n C uw 
Scale [-] 
Figure 1 Required Accuracy for Navigation and 
Automatic Camera Control 
The above figure is based on the assumption that 3% 
overlap error is tolerated in a conventional survey flight. 
Similarly, a ,rule of thumb“ can be used for the 
estimation of the required accuracy for the combined 
block adjustment. 
A zog nu tis 
REQ 0 B 
Typically the measurements of a block adjustment can 
be carried out with a oo of roughly 10 um. The 
corresponding required accuracy (Aago) of the camera 
perspective centers is related to this value via the scale. 
Due to the intersection geometry and the averaging 
effects in a block adjustment a detoriation factor of 1.5 to 
3 may be applied (see also Ackermann [1992]) 
08 
2 0.5 Wee toques NOR LN AN ES cS afi 
S 
= tt 
0.1 NR S A cat AN eue petto sn boa mn Kae 
0 ! ! t f 
1000 2500 5000 10000 20000 50000 
Scale [] 
  
  
  
  
Figure 2 Required Position Accuracy for the Camera 
Perspective Centers in a Combined Block Adjustment 
As it can be seen from the above figures the accuracy 
requirements may vary between a few centimeters to 
hundreds of meters depending on the required scale and 
application. It is obvious that the techniques and the 
hardware requirements to achieve the quoted positioning 
accuracies are also extremely different. Similar to the 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996 
difference in required accuracy, also the operational 
circumstances for the two major photogrammetric 
applications are different. While absolute, real-time 
positioning with medium accuracy is required for 
navigation and camera control, highly accurate post- 
processed positions are required for the GPS based 
aerial triangulation. Table 1 summarizes the operational 
circumstances and the solutions which are provided by 
GPS for the specific application areas. 
  
  
  
  
  
  
  
  
  
Operational navigation + GPS based 
Circumstances | automatic aerial 
camera control ,triangulation 
Required 10-300 m 0.01-1m 
Accuracy 
Movement highly dynamic highly dynamic 
Time of position Real Time Post-Processing 
Differential only limited, with yes 
positioning radio link 
Baseline-Length 10-500 km 10-500 km 
Receiver Update min. 1 Hz min. 1 Hz 
Rate 
Ambiguity not required required in large 
Resolution scale 
applications 
Observation Code only, Phase only, 
Type Carrier smoothed | Carrier smoothed 
code code 
  
  
  
  
  
Table 1 Operational Circumstances for the major 
photogrammetric application areas 
After giving this short introduction to the specific needs 
of photogrammetric GPS applications, the remainder of 
this paper will concentrate on GPS-hardware and 
algorithmic aspects, which are of special importance for 
photogrammetry. 
3. HARDWARE AND SOFTWARE ASPECTS 
Today many GPS receivers are already built for specific 
applications, like GIS data collection, precise static (or 
static like) geodetic surveying, high dynamic or low 
dynamic navigation, or even leisure time applications, 
but there is no receiver on the market which has been 
specifically designed for photogrammetric applications. 
From the photogrammetrists point of view, to choose a 
receiver and the corresponding processing software is 
rather difficult. Especially the highly dynamic 
environment and the stringent accuracy requirements 
over extremely long baselines are not standard 
capabilities which can easily be solved with today's GPS 
technology. To find the appropriate receivers and 
software, which can provide such high precision results 
even under these stringent conditions is rather difficult, 
as also the terms in the data sheets and the quoted 
performance parameters are often misunderstood or 
misleading. (A good overview over today's receiver 
technology can be found for example in van Dierendonck 
[1994]). 
      
  
  
  
  
  
  
   
     
    
      
     
   
  
  
    
  
   
   
   
   
    
   
   
   
   
  
  
   
   
    
    
    
   
   
   
  
    
    
    
   
    
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