# Resolution Aspects for Near-Field Projections
## 2 Materials and Methods
### Subject Study Setup  
To establish an equal subject study environment for all participants, the setup in the light channel is characterized in detail. First, two projection contents were selected for the experimental design: symbol- and text-based content (Figure 1B,C). The graphic illustrates a loading battery symbol (68.5 cm wide and 40.5 cm high) (Figure 1B) and the text 'Welcome to Munich' used the front style Helvetica (93 cm wide and 37.5 cm high) (Figure 1C). Good legibility is the main requirement for a typeface. For this purpose, DIN 1450, for example, specifies the number of criteria [29]. These include typeface, stroke width and thickness and character spacing. However, the symbol-based content or the smallest letter of the text-based projection is designed to fulfill DIN 3864 [30] and guarantee the text's legibility even at a viewing distance of 5 m. Therefore, this results in the used projection sizes of the text or graphics in these tests. Second, the adaptation luminance in the testing room was characterized at 1 m, 3 m and 5 m away from the projection area to guarantee a homogenous ambient lighting condition (Figure 1A). Therefore, in the following work, the scenario with 191-263 lx ambient illuminance is called dusk-/dawn-scenario (DDS), which is the scenario of interest in the first study. This represents the daily usage of a vehicle when the user is leaving for work or coming back home. Of interest in the second study was a scenario with 20-25 lx ambient lighting, which matches the regulation for parking lots with high traffic volume [31], called the parking garage scenario (PGS). Further, it is crucial to ensure a constant Weber contrast, so that the participants will not be influenced by the perceived Weber contrast \(C_{\text{W}}\), which is shown by Equation (1):  
\[C_{\text{W}}=\frac{L_{\text{Projection}}-L_{\text{Background}}}{L_{\text{Background }}} \tag{1}\]  
where \(L_{\text{Projection}}\) states the luminance of the projection and \(L_{\text{Background}}\) is the background luminance of the street's surface [33]. Consequently, the contrast in the dusk/dawn scenario (\(19.60\leq C_{\text{W,dusk/dawn}}\leq 23.53\)) varied slightly no matter what projection content (Figure 1B,C). In the parking garage scenario, the contrast for the battery symbol was constant (\(16.66\leq C_{\text{W,parking,battery}}\leq 17.81\)) (Figure 1B) though the text message showed a decreasing trend for increasing viewing distance (\(23.16\leq C_{\text{W,parking,text}}\leq 49.82\)), which is displayed in the graph in Figure 1C. All contrasts were measured from a first-person perspective with a luminance camera at the three viewing distances and with a measuring height of 1.72 m, which represents an average German person [32], resulting in different viewing angles on the projection area in the analyzed measurements (Figures 1A-C and 2B,C). The viewing angles range between \(59.83^{\circ}\) at 1 m (see Figure 1A) to \(18.98^{\circ}\) at 5 m viewing distance, assuming an average German person [34]. Therefore, the contrasts are valid for the used projection surface, which is smooth and fine-grained asphalt with a luminance  
Figure 1: Schematic illustration of the experimental setup and used projection content in both studies. (**A**) The experimental setup for both studies, where a 3 LCD laser projector [32] is mounted on a vehicle, indicates the three different viewing distances of 1 m, 3 m, or 5 m. Additionally, the observer’s viewing angle to the projection area for the 1 m viewing distance is illustrated. (**B**) Display of the symbol-based projection content and a graph with the contrast measurements in PGS and DDS related to the viewing distance. (**C**) Picture of the text-based content and the graph for the corresponding contrast in PGS and DDS related to the viewing distance. coefficient of 0.03 in the light channel in PGS and DDS (Figure 2A).