Photogrammetry Quality Checks and Statistics

1. Description

In photogrammetry reports‍, messages are provided in case the 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.

2. 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 GSDor no GCPs are used
FAILURE GCPs are used and the GCPs error is more than 2 times the average GSD.

3. Picture Positions

OK

Keypoints Image Scale > 1/4: More than 10,000 keypoints have been extracted per image or Keypoints Image Scale
1/4: More than 1,000 keypoints have been extracted per image

WARNING

Keypoints Image Scale > 1/4: Between 500 and 10,000 keypoints have been extracted per image or Keypoints
Image Scale 1/4: Between 200 and 1,000 keypoints have been extracted per image

FAILURE

Keypoints Image Scale > 1/4: Less than 500 keypoints have been extracted per image or Keypoints Image Scale 1
/4: Less than 200 keypoints have been extracted per image

4. Camera Calibration

OK Perspective lens: The percentage of the difference between the initial and optimized focal length is less than 5%
WARNING Perspective lens: The percentage of the difference between the initial and optimized focal length is between 5% and 20%
FAILURE

Perspective lens: The percentage of the difference between the initial and optimized focal length is more than 20%

5. 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
  • If error in x or y exceeds 2 times the average GSD 
  • If error in z exceeds 3 times the average GSD 

As in the example hereafter:


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