Quality Checks and Statistics
In photogrammetry reports, messages are provided in case that Ground Control Points error does not fall within acceptable tolerances. Picture Positions and Camera Calibration quality is assessed as well. The criteria for each are detailed hereafter.
1. Ground Control Points
Error on GCP is compared to Ground Sampling Distance (GSD) ; error in X and Y shall not exceed 2xGSD ; in Z it shall not exceed 3xGSD.
| OK | GCPs are used and the GCPs error is less than the average GSD |
| WARNING | GCPs are used and the GCPs error is less than 2 times the average GSD or no GCPs are used |
| FAILURE | GCPs are used and the GCPs error is more than 2 times the average GSD. |
2. Picture Positions
| OK | Keypoints Image Scale > 1/4: More than 10,000 keypoints have been extracted per image or Keypoints Image Scale |
| WARNING | Keypoints Image Scale > 1/4: Between 500 and 10,000 keypoints have been extracted per image or Keypoints |
| FAILURE | Keypoints Image Scale > 1/4: Less than 500 keypoints have been extracted per image or Keypoints Image Scale 1 |
3. Camera Calibration
| OK | Perspective lens: The percentage of difference between initial and optimized focal length is less than 5% |
| WARNING | Perspective lens: The percentage of difference between initial and optimized focal length is between 5% and 20% |
| FAILURE | Perspective lens: The percentage of difference between initial and optimized focal length is more than 20% |
4. GCP Warning in Photogrammetry Reports
In Photogrammetry Reports delivered at job completion, the errors are displayed according to the following color chart:
| ORANGE | If error in x or y or z exceeds one time the average GSD |
| RED |
|
As in example hereafter :
