## 2 State of the Art
### Visualization
#### 2.3.3 Visual Design and Perception of 3D/4D Content  
Visual properties of 3D/4D visualizations heavily rely on device capabilities, e.g., screen properties (2D pixel monitors in smartphones, tablets, and desktops; 3D displays such as holographic displays, holograms, and 3D stereo displays; VR/AR headsets), in teraction capabilities (input via mouse vs. touch vs. hand tracking; sensors) and usage scenarios (e.g., location-based vs. remote; mobile vs. desktop) [9; 180]. Regarding design, influencing parameters include the level of detail (LoD), which needs to meet both the task and hardware requirements [210]. Detailed visualizations of historical reconstructions are advantageous for imaginability [211]. On the other hand, they are suspected of distracting scholars from their research questions [212] or causing cognitive overload [213]. There is a long-standing debate about the visualization strategies for 3D/4D reconstructions that are appropriate for historic architecture. The main positions include visual styling--to achieve realistic visualizations that are easy to understand and impressive for viewers--or schematic depictions showing hypotheses and schemes [210; 214; 215]. Visual style is frequently discussed regarding its fit to scholarly recommendations and as a potential distraction for viewers [44]. Since the majority of 3D/4D reconstructions still are aimed to be highly immersive and realistic visualizations [216], the full scope comprises a large variety of photorealistic and non-photorealistic styles [217; 218; 219]. Much research has been performed on the visualization of different degrees of certainty [214; 220; 221; 222]. Current approaches can be roughly categorized into enrichment of representations by explanatory elements [223] and adaptation of representation quality, e.g., LoD or visual styling [210; 214; 215; 224; 225; 226; 227]. Scaling has been frequently assessed as an important parameter for perceiving architecture [210; 228]. Visual acuity is the ability to distinguish details and is mainly influenced by the distance to a virtual or physical object [229; 230; 231; 232]. Perspective depiction and perception include the effect of different fields of view [233; 234; 235]. Lighting refers to the shading of specific parts of an object [236] and is of high relevance for visual comparisons and the realism of virtual visualizations [237; 238; 239; 240; 241; 242]. Color is also highly relevant for perception--in the case of historical objects, it ranges from realistic coloring and scales to code parameters or support, visually distinguishing model parts [243; 244; 245; 246; 247]. Methodologies for investigating the perception of digital visualizations are available but not comprehensively used yet to assess 3D/4D reconstructions. The traditional method is empirical user studies in experimental settings (e.g., [248]). As an extension of this paradigm, several data-driven user observation methods, e.g., eye tracking, are used to verify areas of attention (e.g., [210]). Three-dimensional XR spaces add the methodological challenge of mapping what the user sees, which can be achieved, e.g., via viewshed calculations in fully 3D spaces [232; 249; 250]. Despite much research, the main criticism is that studies of viewer effects are primarily descriptive rather than proven by user tests [230; 251; 252]. The quality of perception is influenced by visual parameters, such as size and shading (c.f., Gestalt theory [253], cognition psychology [254; 255]); cultural settings including visual semiotics [256]; engagement [257]; and psychological processing such as visuospatial reasoning [258; 259; 211] or visual research [256; 260; 261]. User expertise with visualizing specific content is another parameter [262; 263; 264]: \"visuality\" [265], or, more precisely, \"visual competence\" [266] or \"visual literacy\" [267; 268].