Markerless Visual Tracking of a Container Crane Spreader

Crane systems play a crucial role in container transport logistics. This paper presents an approach for visually tracking the position and orientation in 3D space of a container crane spreader. An initial pose estimate is first employed to render a 3D triangle mesh model of the spreader as a wireframe with hidden lines removed. The initial pose is then refined so that the visible lines of the wireframe match the straight line segments detected in an input image. Line segment matching relies on fast, local one-dimensional searches along a segment's normal direction. Matched line segments yield constraints on the spreader motion which are processed with robust parameter estimation techniques that safeguard against outliers stemming from mismatches. The tracker automatically determines the visibility of segments, without making limiting assumptions regarding the spreader's 3D mesh model. It is also robust to parts of the tracked spreader being out of view, occluded, shadowed or simply undetected. Experimental results demonstrating the tracker's performance are additionally included.