Expand with CIE sky model

[khufkens]

Implementing a CIE sky model shouldn't be too difficult. Look up literature and or existing algorithms to complement the current algorithm.

• difficulties might be to find a moon model as CIE is focussed on sun parameters
• does open up the option to include light pollution (https://onlinelibrary.wiley.com/doi/10.1002/ntls.10019)

[khufkens]

The R canopy analyzer has a basic CIE model for daylight

https://rdrr.io/cran/rcaiman/src/R/cie_sky_model_raster.R

Will need to find the moonlight component

[khufkens]

Seems like the CIE model components mainly deal with diffusion on a defined source. Changing from solar to lunar shouldn't be too difficult from the above code if radiative components can be found for the moon.

[khufkens]

https://www.researchgate.net/publication/6318780_Light-pollution_model_for_cloudy_and_cloudless_night_skies_with_ground-based_light_sources

[khufkens]

Illumina light pollution model:
https://github.com/aubema/illumina