Automated positioning of 3D virtual scene in AR-based assembly and disassembly guiding system

In augmented reality (AR)-based assembly and disassembly guiding systems, the guiding effects mainly depend on display characters of virtual guiding scene. If the virtual guiding scene is not displayed properly, such as displaying out of the operator’s view, overlaying on the interest region of the screen, selecting an inappropriate viewpoint of the three-dimensional (3D) guiding scene, and so on, it may disturb normal operation instead of guiding. To display the 3D virtual guiding scene on suitable screen region from a comfortable viewpoint, an adaptive guiding scene display method was proposed. In the adaptive selection of the display region, the display screen was divided into many grids. The screen projection coordinates for vertexes of CAD feature’s bounding boxes, and the occupied index of each grid was calculated. The maximum connected region of empty grids was chosen as a non-interest region on the screen for displaying the 3D guiding scene. In the optimal viewpoint selection algorithm, a viewpoint information measurement operator was put forward, which took projection area, visible proportion, information entropy, and difference in depth of all visible vertexes of CAD feature’s bounding box in 3D virtual guiding scene into account. Finally, based on the principle of perspective projection, the 3D virtual guiding scene was positioned into the virtual world and displayed from the specified viewpoint on the specified screen area. All algorithms proposed in this paper utilized the automatically extracted CAD feature’s bounding box model of part as input data so they could be implemented for online planning of 3D assembly guiding scenes.