Differential Pseudoranges and phases 
  
TX 0,55: m 0,58.m 
Ny 0,51 nm 0,53» 
T2 0,66 m 0,76 m 
  
  
  
  
  
4) Idem, when keeping only an imaginary control point without 
error at the center of the block. 
  
  
Differential Pseudoranges and phases 
Tx 0,65 m 0,62 m 
Sy 0,64 m 0,76 m 
eZ 0,88 m 1,00 m 
  
  
  
  
  
All the notices previously done about Lunel test site are con- 
firmed ; but results with one point appear less good. 
VI) Use of GPS data aerial navigation 
The on-board system allows to determine in real time position 
of the points of view with'an accurdcy of about one meter, dif 
five satellites are used. These data are easily usable for na- 
vigation, in order to calculate and display all the parameters 
needed by the navigator : distance relative to the flight plan, 
remaining distance on a strip, etc. 
Another interesting application is automatic drawing of flight 
indexes. That needs to measure and record roll and pitch of the 
aircraft at the exposure time, in order to determine the coordi- 
nates of the center of the photograph. This operation is done 
with a twin gyros unit, mounted on the camera. Roll and: pitch 
are digitized and recorded on HP 9825. calculator. Such a test 
was done in 1996 on Amiens test site with transfer of the cen- 
ters of the photographs on a 1/25000 map, with an automatic HP 
plotter system. The obtained accuracy is at least as good as 
manual identification. 
The August 20 test flight has brought interesting ideas about 
capabilities of the present GPS configuration. For a photogram- 
metric use we must have five well-placed satellites, always the 
same for the duration of the flight. The Vichy sheet was flown 
with these conditions ; then, other sheets were photographied 
with poorer conditions. GPS receiver operated in automatic mo- 
de : it selected itself the satellites and validated measures 
until an elevation of 0° (instead of 5? in|normal conditions). 
Three satellites could be received until 13h50, what allowed 
satisfactory positions for navigation, better than those obtai- 
ned by any other autonomous navigation means ! With three sa- 
tellites'a position is calculated. using a fourth data : inter- 
nal clock of the receiver, aircraft altitude measured by on- 
board altimeter or a pressure sensor. Accuracy could be enhan-