It is important to consider the following facts:
- At a defined altitude, increasing the focal length:
- A smaller area is captured, and therefore:
- The Ground Sampling Distance (GSD) value will decrease: one pixel will capture a smaller area and therefore the image will have a higher spatial resolution.
- At a defined focal length, 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.
Terrains:
- Forest and dense vegetation: Flying higher helps for the reconstruction, but the spatial resolution will be lower.
- Buildings: Flying higher reduces the artifacts at the building edges, but the spatial resolution will be lower.
Overlap:
- Low altitude with big focal length will request a very high image rate in order to maintain a good overlap.
- For a given focal length and a given image rate, increasing the altitude will increase the overlap.
For more information about selecting the flight plan type, computing the flight height for a given GSD and computing the image rate to get a given overlap: Step 1. Before Starting a Project > 1. Designing the Image Acquisition Plan.
For more information about configuring the camera settings: Step 1. Before Starting a Project > 2. Configuring the Camera Settings.
Hi,
Accordingly to this article, what is the maximal GSD [m/px] and the minimal overlap [%] to get a reasonable 3D map out of images or video ? Thanks.
Hi Alouia,
It depends on the camera, the homogeneity of the area you are capturing etc. You can read this article: https://support.pix4d.com/hc/en-us/articles/115002471546-Image-acquisition to know more about the overlap required. The GSD depends on the focal length of the camera and flight height. You can find the GSD calculator here: https://support.pix4d.com/hc/en-us/articles/202560249.