SOLVING GEOSPATIAL TASKS IN 2D AND 3D VISUALIZATIONS OF MAPS - Information Visualisation: Techniques, Usability and Evaluation - page 230

well as stereoscopic parallax [13]. Following the terminology in [14], the
following definitions for visualizations are used throughout this chapter:
A 2D visualization is conceptually defined as a two-dimensional
graphical model which is positioned in, and aligned with, the 2D plane of
the display. Even for a stereoscopic rendering, using some viewpoint
dependent perspective projection, the 2D visualization will not create any
depth cues (neither linear perspective nor parallax). See Fig. 12.1(a) and
Fig. 12.2(a) for an illustration.
A weak 3D visualization is conceptually based on a 3D graphical
model that is rendered on a two-dimensional display surface. The
presentation on a 2D image plane requires projection of the 3D geometry
onto this plane. The weak 3D visualization assumes a static projection
where the centre of projection is fixed at viewing position VP on the
central axis of the projection plane (compare Fig. 12.1(b)). The resulting
2D image on screen will show central perspective distortion (see Fig. 12.2
(b)). The only spatial cues available to the observer are pictorial cues; they
comprise linear perspective, shading effects, occlusion, relative size, and
others. For a complete list of these so-called monoscopic depth cues, refer
to Kjellin et al. [11]. In the literature, weak 3D is often referred to as 2.5D
or simply 3D.
A strong 3D visualization is conceptually defined by geometry in 3D
space which is rendered using both monoscopic and stereoscopic depth
cues. Dynamic 3D cues (motion parallax) are also provided even for static
objects. Hereby the projections for left and right eyes' views of a moving
observer are continuously updated using head position tracking [15]. Fig.
12.1(c) illustrates the concept of a strong 3D map visualization. Since an
arbitrary viewer position in relation to the projection plane is assumed, a
generalized projection must be applied that allows the centre of projection
to be far off the centre axis of the projection surface, yielding to both
perspective and oblique projection distortions (see Fig. 12.2 (c)).

(a) (b) (c)

Fig. 12.1. Illustration of the conceptual design of a 2D visualization (a) , a weak
3D visualization (b), and a strong 3D visualization (c) of maps.