Automated Quality Control for Ortholmages and DEMs

The checking of geometric accurancy of orthoimages and digital elevation models (DEMs) is discussed. As a reference, an existing orthoimage and a second orthoimage derived from an overlapping aerial image, are used. The proposed automated procedures for checking the orthoimages and DEMs are based on matching of corresponding image patches. Existing topographic databases are additionally used in order to select time-invariant objects as checkpoints. In order to avoid blunders in the correlation, thresholds for similarity measures are applied. Detailed studies show that a combination of thresholds for the maximum correlation coefficient, the average mutual information, and distancecan reduce the number of blunders in the automated measurements considerably and should therefore be applied. The calculation of DEM errors is carried out by an improved formula. The new methods and procedures are applied to two practical examples, and the results are presented.