In this tutorial, we are going to look into the concept of Ground Offset.
Many a times, when you are surveying a vertical structure, such as a building or a housing site, you encounter the situation where you’d like to fly your drone at a fixed altitude, but calculate the much needed overlap with respect to the building roof or structure height as opposed to the ground. This allows you to generate higher quality 2D maps and 3D models as your overlap takes the inherent height of the building/structure into account.
Needless to say, this is also true for structures below takeoff altitude, where you’d like to calculate the overlap with respect to the ground below the takeoff altitude.
In Hammer, this parameter for the mission can be adjusted using the Ground Offset option. Adding a positive ground offset will make Hammer calculate the overlap using the camera’s footprint on the building/structure roof as opposed to the camera’s footprint on the ground. This is visualised below:
Ground Offset is the height of the structure you’d like to survey assuming you took off from the ground (not from the roof of the structure).
The Ground Offset option is available in following Hammer missions:
Inspection: Useful for roof and solar inspections.
Mapping: To capture 2D Orthomosaic maps.
Double Mapping Missions: To capture 3D models.
Altitude and Ground Offset parameters in Hammer
Setting the altitude to 50m, and ground offset to 20m in this example means that the drone will fly at 50m from the takeoff point and calculate picture points by taking the ground offset / building height (20m) into account. Increasing the ground offset will make the plan denser, and decreasing the ground offset will make the plan sparser. This is because the drone’s camera has a smaller footprint on the building’s roof as opposed to the ground, therefore pictures will be taken closer together to achieve the required overlap.
We hope this post clarifies how you can use the Ground Offset in Hammer to improve your 2D and 3D data collection by accounting for the target structure’s height in your flight planning and automation. If you currently do not have access to Hammer, please feel free to download it from the App Store.
We look forward to hearing from you.
— Hammer Missions Team