International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004 
  
2.1 Typical Work flow 
Typically, at Hansa Luftbild German Air Surveys, GPS/INS 
data are used in ortho photo projects or LIDAR. This paper is 
restricted to camera projects only. 
Following the sequence of a GPS/INS project in a 
commercial company, the typical work flow runs as follows: 
| 
Acquisition of the project 
— flight planing 
— survey flight 
— establishment of ground control 
— computation of the projection centers 
—  triangulation of the calibration field 
— computation of exterior orientation 
—  (triangulation of all images) 
— production of final products 
For each of these steps, attention has to be paid to specific 
needs of the GPS/INS project. 
2.1.1 Acquisition Phase: During the acquisition of a project, 
it has to be checked carefully, whether or not GPS/INS 
technically and economically is suitable. 
The project has to have a certain size — a calibration field of 
twelve images does not save much money when the complete 
project covers only 20 to 30 images. An exception to this 
could be very special conditions in the area in question. 
For example: 
- a triangulation block covering small and scattered 
islands, 
— very homogenous areas with no details (ice, sand, 
cg.) 
- inaccessible areas (open pit mining, post war areas 
with land mines, e.g.) 
Some of this cases might even make it necessary, to have a 
calibration field outside the project area, although the project 
is so small. 
  
  
  
Fig. 3. Islands in the Red Sea 
The accuracy is not needed to a extreme high level. 
Using the calibrated orientation parameters directly without 
an overall triangulation, the accuracy on the ground, which 
can be reached, depends mainly on the flying height. The 
angular measurements of the IMU are published by IGI with 
0.005 grades for » and ¢ (roll and pitch) and for x 0.01 
grades. (heading) (AEROcontrol, technical information 
sheet). 
Assuming a flying height of 1000 m, for o and ¢ 0,07 m each 
on the ground and for x 0.15 m, gives a total of about 0,1 m 
for angular measurements only. The expected accuracy of the 
projection centers has to taken into account as well as the 
quality of the DTM data used. 
The score of the project are ortho photos, no measurements 
are involved, e.g. a DTM. 
Using the calibrated orientation parameters directly without 
an overall triangulation, might or might not be sufficient for 
stereo restitution. 
Can the project be done using other techniques? 
The question might sound strange, but sometime GPS/INS is 
the only possible technique to fulfil customers requests 
considering the time planed for the project or the terrain 
involved , e.g.. 
A triangulation of about 1770 images along a planned 
pipeline with some sixty flight lines covering about 770 km 
can be done in six weeks including the establishment of 
ground control. But that was the time, we had from offer to 
delivering finished ortho photo mosaics. 
  
  
|---100 km---| 
Fig. 4. Flight layout for a pipeline planing, Germany 
The customer accepts the technique. 
Even if all parameters are perfectly set up for a flight based 
on GPS/INS, the customer sometimes cannot be convinced to 
use this rather new technique. 
2.1.2 Flight planing is the next step in the procedure. 
Of course, these flights have to be based on kinematic GPS, 
where the distance to the GPS station should exceed 50 km. 
Within Germany, a dense network of permanent public GPS 
base station can be accessed easily. For international 
missions, the base stations have to be mostly organised in a 
sufficient number and quality. 
The layout of the flight has to consider the fact, that turns 
have to be made with less than 20 grades roll, in order not to 
loose the GPS signal. Flight restrictions along national 
borders , e.g. can therefore become a even larger problem. 
Transport of the high-tech equipment can also become a 
problem due to restrictions in export of these technical 
products to certain countries. 
   
  
   
  
  
  
   
    
   
   
   
   
   
    
    
  
    
  
  
  
   
   
  
  
   
   
   
  
   
  
  
    
  
  
  
  
   
   
   
   
  
  
  
   
   
  
   
   
    
  
   
  
   
  
  
  
  
   
  
  
  
   
  
  
  
  
  
  
  
  
  
  
   
    
     
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