Based on the difficulties experienced during aero triangulation and orthorectification of the above imagery, we decided to perform a camera calibration on the imagery acquired with the BAT UAV. Camera calibration is a
process that measures the radial lens distortion, principal point offset, and actual focal length of a camera (Fryer,
1996). Using camera calibration parameters increases the accuracy of the orthorectified imagery and image-derived digital elevation models (Clarke and Fryer, 1998; Remondino and Fraser, 2006).