Image acquisition plan for terrain with height variations

Single flight following the terrain elevation variation (recommended)

It is the recommended method since the GSD will be constant for the project since the height difference between the UAV and the terrain is maintained. Be aware that only some of the flying applications can achieve such flights. For example, the terrain awareness functionality is not implemented in Pix4Dcapture.

Figure 1. Single flight following the terrain height variations.

Multiple flights at different constant altitudes

Perform multiple flights at different altitudes with the flight lines perpendicular to the slope. It is important that there is overlap between the flights. Additionally, the GSD in the overlapping areas between the missions should be similar by a factor of two.

The GSD will be approximately constant for the project since the height difference between the UAV and the terrain is maintained.

Figure 2. Multiple flights at different altitudes.

Single flight at a constant altitude regardless of the terrain changes in altitude (not recommended)

If the height difference between the UAV and the terrain is not maintained (keeping constant flight altitude):

• It will affect the GSD: The GSD will not be the same over the whole project because of the variations in elevation of the terrain. In Figure 3, the GSD is more detailed in area B.
• It will affect the overlap: The overlap will be lower in area B.

Figure 3. Constant flight altitude.