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The International Archives of the Photogrammetry. Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
Figure 4: automated disabling of planned images by GIS 
Boolean operations via a second layer 
3.3 Stabilising strips 
From photogrammetric point of view it is recommended to add 
strips perpendicular or at least freehand to the block for 
stabilizing the Aerotriangulation process. Sometimes this is also 
suitable in case of difficult shaped areas to add a run non 
parallel to cover the area more economically. For that, a free 
tool is available to draw a run where the release points are 
computed in same scale and overlap. This line can be moved 
and edited independently to the normal block, there can be even 
add parallel ones to it e.g. to create a second block with 
correctly sidelapped runs. 
3.4 Terrain model 
In the workflow for planning a mission, a terrain height has to 
be predefined. If this height corresponds with the average 
terrain height, scale and overlaps also are in average. If the 
entered value corresponds with the maximum terrain height, the 
predefined scale is the maximum only at the highest elevation. 
At lower elevations the scale will be smaller, and the overlaps 
may not be sufficient for use. 
Only in some cases particularly in flat terrain, the use of average 
terrain height gives a convenient solution. A better adjustment 
to the terrain can be done in two ways. During the project 
planning and in particular with the flight direction, the terrain 
should be taken into account. It is strongly recommended to 
plan as closely as possible parallel to the contour lines. It makes 
no sense to fly perpendicular cross a valley. If the terrain is well 
structured and the terrain below the runs has a relatively 
homogeneous height, the single strips can be adjusted easily 
with an editing tool. 
A more professional solution is the adjustment via a terrain 
model. AeroTopoL needs the DTM for that in ASCII Grid 
format already in a projected coordinate system. Again, GIS 
assists in creating this format from any 3D data in any 
supported coordinate system. It will create an internal DTM 
format and then to write the ASCII Grid in the target datum. 
SRTM data, which is frequently used for this purpose, can be 
re-projected e.g. from WGS84 to a local projected datum 
(ETRS/UTM). A button in the planning dialogue starts the 
adjustment using DTM. The algorithm needs beside the path 
and name of the DTM one information, which is the range of 
scale. As a standard value is set 80%-120%, which meets the 
standard conditions for tenders, however the user can edit it. 
First operation of the module is to change the photographs 
rectangle to a polygon by inserting three vertexes on every side. 
Finally, the footprint is defined by a perimeter with 16 vertexes. 
Highest priority is to keep the overlap within minimum values, 
keep the scale in the defined range and to adjust the various 
altitudes of the runs as bundles. 
Figure 5: Planning over DTM causes interesting footprints as 
presented with an example with high relief 
The footprints with their sixteen comers are used to compute 
the right overlaps in flight and the sidelap to neighbour runs. 
After validating the scale range, it carries out an adjustment of 
the height of the run. The user may also choose to cut a run and 
create three or more lines out of it on different altitudes. 
When this interactive process is complete, the new footprints, 
lines with altitudes and all other information are shown in the 
map-window. 
A new feature enables the user to export the data to Google- 
Earth to visualise the footprints and the planned projection 
centres as shown on figure 6. This workflow assists in 
communication with clients, especially those not familiar with 
GIS. 
Figure 6: Reobservation of the DTM based planning in Google 
earth 
3.5 Data-Exchange, Planning reports 
The planning process is now complete, and the user can select 
from various export functions. The plan can be saved into a 
topol block with full featured database. It includes the project 
area, the runs and the release points. 
A special export is possible of the points into ASCII including 
datum transformation, which can be used to create waypoints in 
an autopilot. 
A typical GIS feature is the creation of an overlap layer. 
Topological analysis routines are used to detect parts of the 
project area of containing sufficient overlap to satisfy the 
requirements for the GCPs. Effective placement reduces the 
numbers of GCPs needed in the costly exercise of getting 
ground control