# Resolution Aspects for Near-Field Projections
## 5 Conclusions and Outlook  
In conclusion, near-field projections have higher visual acuity requirements for text-based projections compared with symbol-based content. The theory especially states that textual acuity tests demand higher visual acuity than sign-based optotype tests due to the more significant cognitive load of the participant [36]. The resolution requirements for near-field projections disagree with the theory of visual acuity regarding the text- or symbol-based content in DDS for 3 m and 5 m viewing distances. External factors such as variation in the roughness of the street surface or the reflection characteristics of the asphalt due to the various viewing distances and viewing angles may be specific to the automotive sector compared to other applications. Nevertheless, taking the 95% confidence intervals into account, it is possible to find in most combinations an overlap of perceived resolutions in Table 2, which are valid for both projection contents, such as PGS 3 m and DDS 3 m and 5 m. This overlay and the possibility to simplify allows us to focus on safety-relevant situations in future mobility-viewing distances above 1 m. The 3 m and 5 m observation distances will be a widespread use case for safety-relevant projections. A vulnerable road user, such as a pedestrian or cyclist, has to be warned by a safety-relevant projection in hers/his field of view and still has enough time and distance to the vehicle to interact with the symbol- or text-based message to avoid any fatalities. The importance of these use cases is likewise emphasized by the report of DEKRA, which states a cycling braking distance of about 4 m to 5 m depending on the braking system and if the road is wet or dry [45]. To create a realistic setting and thus ensure external validity, we instructed the participants to evaluate the perceived quality of the projection instead of solely focusing on the resolution. Moreover, we used automotive-specific symbols and texts instead of symbols typically used in acuity testing, e.g., Landolt rings. The results in Table 2 are indicators for high-quality resolutions for near-field projections and should be considered in the design of near-field projectors. Future studies should investigate if those indicators apply in different contexts, too. However, these findings are the first indicators in the introduced field of research, which can motivate other researchers focusing on future mobility solutions to concentrate on this application field. Especially other research facilities can confirm the discovered relations and increase the importance of this benchmark. A generalization of the study results on every text- or symbol-based projection must be carefully examined. Especially for safety-relevant projection content in an urban environment, further research is needed. The static laboratory setting in this work did not include the movements of either the participant or the vehicle, which derogates the conditions of a realistic urban setting. Next, the theoretical derivation based on the subject study should lead to a verification study, where the displayed study aperture evaluates the resulting resolution requirements in a field test and the requirements for the optical system of the near-field projector. Furthermore, the effect of age or sex, which are possible impact factors for visual acuity, is neglected in this work to establish general resolution requirements. Further, the influence of the font style or complexity of characters [46], which is a stylistic characteristic and language dependent, must be considered when focusing on text-based projection content, such as text-based information of the highly automated vehicle or welcoming messages. **Author Contributions:** Conceptualization, A.S. and T.Q.K. ; methodology, A.S. and T.Q.K. ; software, A.S.; validation, A.S.; formal analysis, A.S.; investigation, A.S. and T.Q.K. ; resources, A.S.; data curation, A.S.; writing--original draft preparation, A.S.; writing--review and editing, A.S. and T.Q.K. ; visualization, A.S.; supervision, T.Q.K.