Combining two-dimensional and three-dimensional views for visualization of spatial data

This research compares two-dimensional (2D), three-dimensional (3D), and 2D/3D combination displays (orientation icon, ExoVis, and in-place) for visualization of 3D spatial data. Both 2D and 3D views can be valuable for different reasons. 3D views can provide an overview of a 3D space, illustrate the 3D shape of objects, and support 3D navigation. 2D views can reduce occlusion of specific parts, show undistorted angles and distances, and enable precise positioning and navigation. Combining 2D and 3D views is valuable when benefits of 2D and 3D are both relevant to the task. First, three 2D/3D combination displays were compared in terms of physical integration of views, occlusion, deformation, flexibility, screen space requirements, and viewing angles. Orientation icons (i.e., 2D and 3D views separated into different windows) offered high flexibility, non-oblique viewing, and low occlusion and deformation, but required substantial screen space and had poor integration of 2D and 3D views. In-place displays (i.e., clip and cutting planes) were the opposite. ExoVis displays (i.e., 2D views surrounding a 3D view in the same scene) had better integration than orientation icons, but greater flexibility and less occlusion and deformation than in-place displays. A theory describing when orientation icon, ExoVis, and in-place displays would be useful was then developed, and experiments that compared 2D displays, 3D displays, and 2D/3D combinations for mental registration, relative positioning, orientation, and volume of interest tasks were performed. In-place supported the easiest mental registration of 2D and 3D views, followed by ExoVis, and lastly orientation icon displays. 3D displays were effective for approximate navigation and positioning when appropriate cues (e.g., shadows) were present, but were not effective for precise navigation and positioning except in specific circumstances (e.g., with good viewing angles). For precise tasks, orientation icon and ExoVis displays were better than 2D or 3D displays alone. These displays had as good or better performance, inspired higher confidence, and allowed natural, integrated navigation. In-place displays were not effective for 3D orientation because they forced users to frequently switch back and forth between dimensions. Major factors contributing to display preference and usability were task characteristics, personal strategy, orientation cues, spatial proximity of views that were used together, occlusion, oblique viewing of 2D views, and methods used to interact with the display. Results of this thesis can be used to guide designers to choose the most appropriate display technique for a given task.