frudawski

# getskytype

The getskytype function determines the CIE general standard sky type for a given luminance distribution of a Tregenza hemisphere. The function can operate in two different modes: The ‘tregenza’ mode (Tregenza 2004) where the whole hemisphere is consideredand and the ‘kobav’ mode (Kobav et al. 2012) which only considers certain parts of the hemisphere. The Tregenza method is more accurate for full data sets but the Kobav et al. method is better suited for incomplete data sets. Both determination methods are available as indipended functions and can be used directly.

[sky,RMS] = getskytype(L,sunaz,sunel,mode,parameter)

Where:

Examples

Determine skytype at \alpha_S = 166\degree and \gamma_S = 33\degree with ‘tregenza’ method:

L = ciesky(12,166,33);
[sky,RMS] = getskytype(L,166,33,'tregenza')

Result:

sky = 12
RMS = 0

Determine skytype at \alpha_S = 166\degree and \gamma_S = 33\degree with ‘tregenza’ and ‘mean’ method:

L = ciesky(12,166,33);
[sky,RMS] = getskytype(L,166,33,'tregenza','mean')

Result:

sky = 12
RMS = 0.2285

Note: the differences to reference sky modell in terms of RMS are due to the different determination method ‘mean’.

Determine skytype at \alpha_S = 166\degree and \gamma_S = 33\degree with ‘kobav’ method:

L = ciesky(12,166,33);
[sky,RMS] = getskytype(L,166,33,'kobav')

Result:

sky = 12
RMS = 0.019045

References

ISO 15469:2004(E)/CIE S 011/E:2003: Spatial Distribution of Daylight - CIE Standard General Sky. Commission Internationale de l'Éclairage (CIE), Vienna Austria, 2004.

Peter Roy Tregenza: Subdivision of the sky hemisphere for luminance measurements. In: Lighting Research and Technology, vol. 19, no. 1, pp. 13-14, 1987, (DOI: 10.1177/096032718701900103).

Peter Roy Tregenza: Analysing sky luminance scans to obtain frequency distributions of CIE Standard General Skies. In: Lighting Research and Technology, vol. 36, no. 4, pp. 271–281, 2004, (DOI: 10.1191/1477153504li117oa).

Kobav M, Bizjak G, Dumortier D.: Characterization of sky scanner measurements based on CIE and ISO standard CIE S 011/2003. In: Lighting Research & Technology, vol. 45, no. 4, pp. 504–512, 2012, (DOI: 10.1177/1477153512458916).