Near-automated orthorectification of archived aerial photographs

Abstract

The proposed objective was to develop a near-automated workflow for orthorectification of archived aerial photographs that overcomes the limited resources problem. Automation was implemented using the oriented fast and rotated brief (ORB) and random sample consensus (RANSAC) for conjugate points detection. Because it is difficult to determine the RANSAC threshold, the RANSAC threshold search for two step triangulation method was developed to find the threshold that resulted in the minimum three-dimensional misclosures at check points from the threshold candidates. For triangulation, the bundle block adjustment (BBA) with a minimal constraint and the absolute orientation were implemented. Although the absolute orientation still requires manual measurement of control points, the required number is usually less than that of traditional BBA, especially for longer strips. The control points were measured in relatively recent high-accuracy orthophotos and the digital elevation model. In the experiments, the archived aerial strip photographs were orthorectified using a differential rectification method with ∼1 m resolution. The first and second orthorectification experiments showed 1.31 m (X), 1.14 m (Y), and 1.88 m (X), 1.51 m (Y) of RMSE. The proposed workflow suggested is significant because it can save cost, time, and labor required for the orthorectification of archived aerial photographs while achieving reasonable accuracy.