Accuracy of automatic aerial triangulation with bundle block adjustment on large historical image blocks in mountainous terrain

Abstract

Achieving accurate orthorectification is a major constraint to upscaling the use of historical aerial imagery for 20th century change detection. This paper presents a series of aerial triangulation bundle block adjustment post-processing model tests to determine the planimetric accuracy obtainable for large historical image blocks, which inherently contain film deformations e.g. warpage and shrinkage. Photo jobs with a range of photo numbers (12-237 images) and area coverage (>33 000-~150 000ha) were included. Self-calibration with 44-parameters and fixing the model to the ground control network achieved the highest final planimetric accuracy (total root mean square error [RMSE] ranging from 18.6 – 25.7px [7.1 – 21.8m] at ground control points and 20.5 – 27.7px [7.8 – 23.5m] at checkpoints). Allowing movement in the model by increasing standard deviations at ground control points or automating the removal of blunders in the model significantly reduced final planimetric accuracy. Removing automated points and running post-processing with no self-calibration also increased the error at checkpoint locations. This study shows that automatic aerial triangulation can assist towards reducing the number of ground control when orthorectifying large blocks of historical aerial photos. However, the study highlights the importance of post-orthorectification accuracy assessment because aerial triangulation accuracy results were not a correct reflection of the error in final orthoimages. Further work should focus on attempting to increase final planimetric accuracy by adjusting the accuracy and number of manual tie points and ground control in combination with altering the amount and positioning of automatic tie points.