Ground Sampling Distance
The Ground Sampling Distance (GSD) is the distance between two consecutive pixel centers measured on the ground. The bigger the value of the image GSD, the lower the spatial resolution of the image and the less visible details. The GSD is related to the flight height: the higher the altitude of the flight, the bigger the GSD value.
Even when flying at a constant height, the images of a project may not have the same GSD. This is due to terrain elevation differences and changes in the angle of the camera while shooting. Since the orthomosaic is created using the 3D point cloud and the camera positions, an average GSD will be computed and used.
Forest and dense vegetation: Flying higher helps for the reconstruction, but the spatial resolution will be lower.
At a defined focal length (for UAV/Drone fixed camera), decreasing the altitude:
- A smaller area is captured, and therefore:
- The GSD value will decrease: one pixel will capture a smaller area and therefore the image will have a higher spatial resolution.
- The image rate needs to be increased to maintain a good overlap.
Picture Overlapping – Recommendation
It is recommended by many people outside there based on their flying experienced where image overlapping ranges from 60% to 90%. We always use 80% for easier setup.
Determining Fly Height
Getting help from the Google Earth is the best choice.