Flight planning for aerial photogrammetry projects involves determining the optimal camera positions and image scale to efficiently cover the region of interest at the desired accuracy. Key parameters include image overlap, ground control point pattern, and block size. Larger overlaps and more observations per point improve accuracy. Modern projects use 80% along-track and 60% cross-track overlaps, providing 10-15 observations per point. With GPS support, ground control points are mainly needed at block boundaries for registration and camera calibration. Empirical formulas can estimate planimetric and height accuracies from image scale and ground sample distance.

1. Flight Planning

2. Aerotriangulation
• Application of photogrammetry
• strength is efficient coverage of lerger areas
• thus blocks with many images required
• larger blocks have thousands of images
• Flight planning
• given a region of interest to be surveyed
• how should the images be taken in order to cover the region at the
desired accuracy?

3. Aerotriangulation
• Arrangement of images for aerial
photogrammetry
• restrictions due to flight path
• regular raster of images (“image block”)
• special cases (e.g. linear mapping of
corridors)
(flight) strip
along-track overlapcross-track overlap
baseline
strip spacing

4. Aerotriangulation
• Advantages
• fewer control points → less terrestrial surveying effort
• higher accuracy because of large number of tie points
• higher reliability: complete redundancy exploited
Efficiency
• tie point measurement (without interpretation) cam be fully
automated
• significantly fewer ground control points needed (for modern
GPS-supported blocks only 4-8)
• Standard method
• nowadays all photogrammetric projects are solved via
aerotriangulation, other procedures are no longer in use

5. • How shall the flight be carried out to reach the
specified accuracy?
• large theoretical and practical studies
• derived from those studies, simplified rules-of-thumb for planning
• most important parameters
- which camera positions?
- which image scale?
• Orientation is performed by joint least-squares
adjustment of all images (“bundle adjustment”)
• detailed treatment in Photogrammetrie 2
• here: rules-of-thumb without derivation
• Goal is to develop a basic understanding for practical accuracies of
photogrammetric surverying
Projekt planning

6. Image blocks
• Classical block setup
• 60% along-track overlap
• 20% cross-track overlap
• 2-6 observations per point
• “Modern” block setup
• 80% along-track overlap
• 60% cross-track overlap
• (or even more)
• 10-15 observations per point

7. Image blocks
• Flight planning
• the actual overlaps are usually larger than the nominally required
ones, to have a safety margin for navigation uncertainty and
varying terrain height
• Large overlaps have become, or will soon become, the norm
• in a fully digital and automated process no additional cost
• Advantage: higher redundancy (DSM generation), lower
distortions (orthophoto)

8. Ground control points
• Classical setup
• 60% along-track overlap
• 20% cross-track overlap
• Control point pattern
• Full GCPs at block borders
• Chains of height GCPs
• in practice usually full GCPs (GPS)
• exception: points with badly defined planimetric location
XYZ control point
Z control point
tie point
projection center

9. Ground control points
• Classical setup
• 60% along-track overlap
• 20% cross-track overlap
• Control point pattern
• Full GCPs at block borders
• Chains of height GCPs
• in practice usually full GCPs (GPS)
• exception: points with badly defined planimetric location
ca. 3 km

10. Ground control points
• Theoretical accuracies - planimetry
• GCPs only required at block boundaries - point inside the block
do not help
• Distance between GCPs influences accuracy of estimated 3D
points at the border (good: GCPs every 4-6 baselines)
• Planimetric accuracy inside block very homogeneous, and
decreases slowly with increasing block size
•
[Ackermann, 1966]

11. Ground control points
• Theoretical accuracies - height
• Classical setup: height GCPs in strip overlap (Toblerone-effect)
• >60% cross-track overlap
• no height GCPs inside block required
• orientation between neighboring strips is stable (c.f. “classical”
along-track overlap)
20%
Q
60%
Q

12. Ground control points
• Theoretical accuracies - height
• Classical setup: height GCPs in strip overlap (Toblerone-effect)
• >60% cross-track overlap
• no height GCPs inside block required
• orientation between neighboring strips is stable (c.f. “classical”
along-track overlap)
20%
Q
60%
Q

13. Ground control points
• GPS/IMU Support
• In GPS-supported aerotriangulation the projection centers become
control points → accuracy independent of block size
• GCPs only required at beginning and end of block
- registration into to world coordinate system
- checking the camera constant (height!)
• GPS with cross-strips: 8 GCPs in block corners
• >60% Querüberdeckung
• 4 GCPs in block corners
• Note: relation to world coordinate system has very little redundancy
G
PS
20%
Q
G
PS
60%
Q
G
PS
20%
Q

14. Accuracy
• Empirical formulas for project planning
• with correct block geometry and GCP pattern the
measurement accuracy is directly mapped to object space
• Planimetric accuracy better than height
• Influence of systematic errors and redundancy
• Sclaing with image scale
• Measurement accuracy of image points
• M·σ ... measurement accuracy on the ground, e.g.
• GSD = 15 cm, σ = ⅓ Pixel → M·σ = 5 cm
σXY = 1.5 · M · σxy σZ = 2.0 · M · σxy
M·σ
σ

15. Measurement accuracy
• Accuracy of observed image points
• with correct GCP pattern and correct processung, the only
influence factor is the image scale
• Measurement accuracy depends on
• definition uncertainty of points
• image quality
• lighting conditions
• automatic/manual measurement
• Empirical accuracy
• for well-defined points 0.3-0.7 Pixel, depending on conditions
• Note: often clients specify a maximal allowed inaccuracy, then
calculate with 3σ ≈ 1.0-2.0 Pixel
• relevant points oftne have high definition uncertainty (e.g. road
boundary, tree, Strassenrand, Baum, gable roof, ...)