Calibration of images that contain large portions of water bodies is challenging. It is recommended to increase the overlap and making sure that some land is visible in the images.
Images that capture only water cannot be calibrated (optimize the internal and external orientation of the camera). The reason is that it is very hard to find keypoints on water surfaces as the water is very uniform and reflective. Even if keypoints are found, it is very hard to match them between images, as these points are not static (water moves).
Since the images that contain only water do not get calibrated, they do not contribute at all to the processing and can not be used to give color to the orthomosaic. Therefore, there might be holes (lack of information) in the orthomosaic on water surface areas.
It is suggested to adjust the flight plan and:
- Increase the flight height to cover a larger area with a single image.
- Increase the overlap.
- Images should contain at least 30% of land.
In this case, the images could get calibrated and contribute to the orthomosaic generation. For more information about how to map water surfaces: Step 1. Before Starting a Project > 1. Designing the Image Acquisition Plan > a. Selecting the Image Acquisition Plan Type.