# Calculation of View Factors for Building Simulations with an Open-Source Raytracing Tool
## 7 Conclusions  
The primary aim of this research was to demonstrate the methodology of employing RADIANCE as a view factor calculation tool. As illustrated through the several examples for finite and differential surfaces in Section 3, RADIANCE can be effectively used to calculate view factors for a variety of surfaces through the standard Monte Carlo method. View factors can be calculated with only a couple of the over 100 programs that are present in the RADIANCE suite. So, the steep learning curve that has traditionally been associated with using RADIANCE for lighting calculations is not applicable to the calculation of view factors.  
As discussed previously, a majority--if not all--of the view factor calculation tools developed in the past few decades are currently not under active development. Consequently, the functionalities of these tools have not been updated to leverage the advancements in computing hardware and operating systems. In contrast, RADIANCE is still being actively developed and maintained by its core developer as well as the principal funding agency. This is attributable partly to its relatively large user base and prominence as an industry- and research-grade simulation tool. RADIANCE can be used on multiple operating systems and computing platforms such as commercial cloud-based computing systems.  
The primary advantage for RADIANCE, when compared to existing view factor calculation tools, lies in its ability to efficiently handle complex geometries that are likely to be found in building simulations in both indoor and outdoor contexts. Conventional radiosity-based tools typically support only planar shapes and require extensive calculation time. As shown by the examples in Section 3, irrespective of the shape and size of a surface, RADIANCE provides a singular approach for calculating view factors. Furthermore, the availability of free plugins and translation tools to export geometry from common building 3D modeling software to RADIANCE makes it possible to generate, and calculate, view factors for virtually any scale and form of surfaces.  
The calculation methodology proposed in this research can be applied to tools such as EnergyPlus and ESP-r to incorporate complex, non-planar shapes into building energy simulations. Currently such tools rely on approximating complex building geometry generated through 3D modeling software such as Revit and Rhino3D into simple planar surfaces. Several studies have already documented the coupling or co-simulation of RADIANCE with building energy simulation tools for performing more physically accurate lighting simulations with complex geometries. Similarly, in such workflows the calculation of view factors too can be performed through RADIANCE by either using the same model from lighting simulations or exporting a dedicated model through one of the freely available open-source translators.  
The authors intend to disseminate the automation scripts for calculating view factors through 3D modeling software on open-source platforms. Future research will address the application of this tool to simultaneously calculate view factors of multiple surfaces and validate the examples with obstructions by comparing them with analytically derived solutions.  
Conceptualization, S.S.; methodology and software, S.S. and G.W.; formal analysis and validation, S.S. and S.T.; writing--original draft preparation, S.S and S.H.; writing--review and editing, S.S., S.H., S.T. and G.W.; supervision, S.H., S.T. and G.W. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare that they have no potential conflict of interest regarding this research work.