# Resolution Aspects for Near-Field Projections
## 2 Materials and Methods
### Subject Study Setup
Additionally, a classification of the angle-dependent reflection behavior S according to the CIE standard was made, which corresponds to a diffuse scattering surface (S < 0.4) for the PGS (S = 0.09) and DDS (S = 0.09) scenario [35]. A post-study questionnaire asked the participants if any glare was perceived during the testing procedure to ensure that the study environment was appropriately defined for all subjects. The results of this question for the DDS and PGS are displayed in Figure A1. These assure that the subjects do not perceive glare, as none of the subjects stated so in the questionnaire responses. Furthermore, to ensure that the projection surface is suitable for evaluating projection qualities, a pre-study took place to evaluate the smallest resolvable detail on the street's surface. The subjects' task was to confirm whether they could see one or two lines where eight different gap widths were repeated randomly three times, corresponding to the constant stimuli method. This procedure was the same for the PGS and DDS scenarios at a viewing distance of 1 m, which is the most critical viewing distance from which to evaluate the smallest resolvable detail. The smallest resolvable detail relates to a standard visual acuity test task, such as a Landolt ring task [36]. In the subject study, the line pairs rotated 45, 90, or 180 degrees, so subjects would have a variation and thus no learning effect during the study. Eight subjects between 27 and 60 years participated in the pre-study. The resolution of the gap between the two lines was 85.73 px/\({}^{\circ}\) for PGS and 52.93 px/\({}^{\circ}\) for DDS. Consequently, every participant had about 10 min to adapt to the ambient luminance in every scenario, which guarantees the activation of the rods in their sensitivity [36], so the illustrated projections do not discomfort the subject. The participants used a modified keyboard, where just the keys N and Y were accessible, since the other keys were removed. Finally, after the introduction, the participants had to log in their subjective answers by pushing the key Y when perceiving a high-quality resolution and pressing the key N if the quality did not meet individual quality requirements. The keyboard is connected to a computer via a USB cord to guarantee no potential latencies. The visual stimulus presentation and data handling is implemented in Matlab R2018b with the graphical toolbox Cogent 2000 version 1.33 [37]. All instructions, experiments and the questionnaire used the German language. The study design was mixed between-within-design with ambient lighting being the between-subjects-factor and the projection content and viewing distance being the within-subject-factors. Figure 2: Extract of the study and examples of luminance measurements. (**A**) Participant at 3 m observation distance to the projection area in the DDS. The observed projection content consists of the battery symbol on the fine-grained asphalt. (**B**) Luminance measurement of the symbol-based projection in the PGS from a first-person viewing perspective of 3 m [34]. (**C**) Luminance measurement of the text-based projection in the PGS from a first-person viewing perspective of 3 m [34].