There is more than one block of calibrated images after processing step 1 in PIX4Dmapper.
A block is a set of images that were calibrated together. Multiple blocks indicate that there were not enough matches between groups of images to provide global optimization. When a project contains multiple different blocks they may not be accurately georeferenced relative to each other. A project should ideally contain only 1 block. See below for how to check the number of blocks within the quality report.
On the left, the existence of two blocks of calibrated cameras is highlighted in the Quality Check table. On the right, the cameras that have been calibrated by block are shown in colors (yellow and green) in the 2D Keypoints Matches graph.
There are several causes that can lead to this issue:
- The project consists of multiple flights which were flown at different periods, different heights, with different cameras.
- There is not enough overlap between image acquisition plans.
- Corridor projects can exhibit this issue if images were not acquired correctly.
- The terrain is flat with homogeneous visual content such as agriculture fields or snow, sand, and water.
- The project area consists of forest and dense vegetation.
- Incorrect calibration method for the terrain and image dataset.
Possible solutions to the previosly listed causes are proposed below.
For cause 1:
- The flight height should not be too different between the flights, as different height leads to different spatial resolution. For more information: Can PIX4Dmapper process Images taken at different Flight Heights?.
- Try to fly with the same lighting conditions, same hour of the day, same sun direction, same weather conditions.
For cause 2:
- Make sure that each plan captures the images with enough overlap.
For cause 3:
- Corridor mapping datasets should consist of at least 2 lines of flight with high overlap.
- It is also recommended to have image geolocation. It is highly recommended to have GCPs well distributed in the model: Number and distribution of ground control points (GCPs) in corridor mapping.
For cause 4:
- Process with lower Keypoints Image Scale: This processing option can lead to a higher number of calibrated images than the default original keypoint image scale. For more information: Menu Process> Processing Options... > 1. Initial Processing> General.
- Enable Geometrically Verified Matching.
For cause 5:
- Process with lower Keypoints Image Scale: This processing option can lead to a higher number of calibrated images than the default original keypoint image scale. For more information:
- Menu Process> Processing Options... > 1. Initial Processing> General.
For cause 6:
- Verify that the calibration method used for step 1 is appropriate for your project.