# Virtual Reality for Spatial Planning and Emergency Situations: Challenges and Solution Directions
## 4 Results
### User Experience Considerations  
The optimal frame rate identified in the review process for a smooth VR experience is 90 frames per second (fps). When dropping below 90 fps, a VR experience often causes discomfort or nausea (cybersickness), and it makes the experience less immersive [26]. The same authors give two solutions to achieve a higher frame rate. They describe this optimization as an iterative process, in which a performance bottleneck first needs to be identified. When it is identified, measures should be applied to improve performance. Two common bottlenecks are clusters with a high rate of polygons or materials and objects rendering when they are not visible. For the clusters, a dedicated script can be applied that  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Paper** & **3 ds Max** & **Revit** & **Blender** & **AutoCAD** & **Maya** & **Unity** & **Unreal** & **HTC Vive** & **KAT VR** & **Oculus Rift** \\ \hline [16] & x & & & x & & x & & x & & \\ [28] & x & & & x & & x & & x & & \\ [29] & & x & x & & & x & & x & & x \\ [30] & & x & & & x & & x & & & x \\ [22] & & & & & x & & x & x & & \\ [31] & & x & & & & x  
detects the clusters, and once detected, they can be simplified. The second bottleneck can be mitigated by excluding objects that are not visible from rendering. This was achieved by [34] through the use of the Occlusion Culling algorithm. They also used lightning to optimize their application. Next to the frame rate, the speed and the way of walking of the FPC controller strongly influence the user experience to a high degree.  
[PERSON] et al. [31] set a speed of 2.5 m/s for two reasons: a higher speed can cause motion sickness and a lower speed can make the experience boring and decrease the participants' tension. Therefore, the authors outline that 2.5 m/s should be considered by others as a default walking speed for future research applications. To be able to move the FPC, the simplest method is to use the buttons on the VR controller. However, three papers [26; 30; 35] made use of the swing of the participants' arms to move in order to increase immersion. To make the VR experience more realistic, three other aspects were added in the selected papers: To make the situation look like a real evacuation, non-player characters (NPCs) could be added to the application. [PERSON] et al. [20] found that these NPCs caused a higher sense of emergency in their participants. The study in [33] developed a pipeline that explains the development and animation of NPCs in detail. Further, [16; 28; 29; 31; 32; 33] added smoke and fire. The smoke and fire can be created with Blender or using the particle system effect that is available in Unity. In addition, [22] included a realistic 3D alarm soundscape, which proved to have a positive influence on the reality perceived by their participants.  
When all the user experience is implemented, the application should be, of course, tested. [PERSON] [26] emphasize the importance of this technical pretesting and state that it could take up to 20% of the development time for the application. The pre-testing should be carried out with real participants, but it does not have to be the full experiment. Select components of the application can be tested, and participants can answer questions and give feedback using an offline questionnaire. After testing, the application is finished, and it can be used for collecting results.