Remote estimation of target height using unmanned air vehicles (UAVs)

Abstract

Estimation of target height from videos is used for several applications, such as monitoring agricultural plants growth or, within surveillance scenarios, supporting the identification of persons of interest. Several studies have been conducted in this domain but, in almost all the cases, only fixed cameras were considered. Nowadays, lightweight UAVs are often employed for remote monitoring and surveillance activities due to their mobility capacity and freedom for camera orientation. This paper focuses on how the height could be swiftly performed with a gimballed camera installed into a UAV using a pinhole camera model after camera calibration and image distortion compensation. The model is tailored for UAV applications outdoor and generalized for any camera orientations defined by Euler angles. The procedure was tested with real data collected with a regular-market lightweight quad-copter. The data collected was also used to make an uncertainty analysis associated with the estimation. Finally, since the height of a person who is not standing perfectly vertical can be derived by relationships between body parts or human face features ratio, this paper proposes to retrieve the pixel spacing measured along the vertical target, called here Vertical Sample Distance (VSD), to quickly measure vertical sub-portions of the target.