The International Archives of the Photogrammetry. Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beiiing 2008 
4. MISSION NAVIGATION 
4.3 Navigation and control 
When the FMS is built around GIS capability, the user has the 
benefit that data from GPS are handled properly and displayed 
immediately on a moving-map window and/or to virtual 
instruments. The moving map functionality using rasters and 
vectors as well as the real time computation of the real 
measured footprints are compelling benefits to survey pilots, 
providing an intuitive and easily scanned interface for 
information from the system and some guidance to flight 
operations. The position and rotation of the camera can be used 
and calculated to adjust to the terrain, ensuring proper coverage 
and overlap in the project. If some areas seem to be badly 
overlapped or covered, manual imaging can avoid the necessity 
of additional flights. 
Mobilisation for data capture can only be done when weather 
conditions are suitable and is expensive in addition. 
Confirmations of the status of the mission, the certainty of 
image capture are critical to effective mission execution. 
4.1 Camera-definition and Auto zooming 
In many cases, the camera is properly defined during planning 
as a frame camera in either landscape format or portrait format. 
This is essential for a proper mission plan. In the navigation is 
the possibility only to rotate the camera by 180 degree. This 
will conform with the mission plan but not with the kappa angle 
of the image. The orientation of the camera can be defined here 
and will be taken into account during writing the report files. 
For control of the mission and the navigation, moving map 
function is used to display raster and vector-data, the planned 
runs and release points and the own position with orientation. 
Typically, the project area is distant from the starting and 
landing point. It is useful to have the virtual instruments as a 
navigation guide, assisted by the auto-zoom function as the 
plane approaches the project area. The zoom levels can be 
defined (minimum scale, maximum scale) and the rate of refresh 
levels. 
4.2 Sequencing and catchments 
Automatic shutter release is achieved by calculating the distance 
from the target to the true present position of the camera. The 
refresh rate of the position typically is 10 Hz due to the speed of 
the GPS/IMU. 2 snap-circles are defined as inner and outer 
buffer. The inner buffer starts a release when the GPS position 
is detected as inside this buffer; the outer buffer monitors the 
nearest position of the aircraft to the planned release centre. The 
sequence of the runs and their direction can be preset which 
reduces any interference during flight. Some additional 
functions can be set up, especially if a stabilizer is used and a 
full heading compensation is required. 
Figure 7: Setup of 
the run-sequence 
and the snap 
parameters 
The heart of the entire system is the carefully developed 
combination of software and hardware. The avionic hardware 
consists of synchronized GPS data with INS information. Rapid 
update and event based additional position and attitude 
information is handled by the FMS. It is recommended that the 
setup include a rugged notebook and a monitor for the pilot. 
The pilot-display is important; it should be visible even under 
daylight conditions, small enough to be mounted in the cockpit 
along with the other instruments and in easy view of the pilot. 
The control of the camera via the hardware uses both the release 
signal from the software and the event signal returned from the 
hardware as confirmation. 
The entire communication between FMS and Hardware/camera 
is managed by one serial cable only, using high-speed 
bidirectional serial communication. 
The incoming data is, on datum WGS84, the commonly used 
datum in GPS applications. They are transformed on the fly into 
the user-selected datum of the map window. 
Instruments placed in a control panel show the pilot an artificial 
horizon, a track-guidance with the offset parameters and the 
heading and a target-assistance to catch the snap-point in 3d. 
Besides these instruments, the pilot sees his position, 
represented as a aircraft symbol over the raster and vector data. 
The orientation of the aircraft is shown by the coordinate 
differences during moving. * 
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Figure 8: Moving map and virtual instruments support a précisé 
navigation 
The auto-zoom function always assists in navigation to the first 
navigation point. Beside that, the software always computes on 
a high priority task the distance to the next release-point. The 
software enables only the image that is next in the strip, or next 
in the project. The virtual instruments guide the pilot to the next 
snap point. If the outer snap radius is reached, the system is 
enabled to release the photo and tries to detect the closest point 
to the inner snap-circle. If the computed distance starts to 
become bigger, the system fires the image while the software 
sends a command to the port. The camera releases and creates 
an impulse to the sensor, which informs the software again to 
store the data (y, x, z, roll, pitch and heading). AeroTopoL 
calculates by these values an actual footprint that is shown on 
the map with the real projection centre in the middle. 
In this way, the coverage of the data can be monitored easily. If 
all images are taken, analyses over the correct overlap can be 
done immediately to see, if additional photos are needed. This 
function is the same as at the planning part, just there are used 
the real measured values of X,Y,Z, Omega, Phi and Kappa for 
the footprints. 
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