An outlier tie point is a point on the ground which has corresponding image points that are do not depict the same feature in each image. These points have large re-projection errors and degrade the entire quality and accuracy of the outputs being generated by OneButton. This document will show the user how to remove outlier tie points using OneButton Professional.
Before deleting the outlier tie points the user will need to perform a bundle block adjustment on their project (section 5.3 in the User Manual or the “How To: Perform Bundle Block Adjustment” article) using OneButton Professional.
How-To: Remove Outlier Tie Points
- Navigate to the Points tab in the main OneButton Professional window.
- In this tab, clicking on the “Max Pixel Residual” column title to sort the table accordingly (Figure 1).
Figure 1 - The red arrows shows the "Max pixel residual" column
3. Sort the “Max pixel residual column” in descending order so the highest values are at the top. The value represents the re-projection error which is associated with this point and a higher value means that the point has a higher error. The points that have significantly higher values than the rest of the points in the list are considered outliers (Figure 2).
Figure 2 - The highlighted value shows a tie point that is considered an outlier
4. It is recommended to review the outlier tie points as follows:
a. Select the outlier tie point from the tie point list
b. Open the image viewer and review the locations where the point appears in each image
c. If the point is shown in two different features in each image (Figure 3) it is an error and should be deleted.
Figure 3 - The image viewer shows where the selected tie point is located in each image. Notice how the tie point is shown on two different features which causes a high re-projection error
5. To delete the point, right click on the point and select "Delete" from the context menu.