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tregenzaskytype

The tregenzaskytype function determines the CIE general standard sky type for a given luminance distribution of a Tregenza hemisphere. Contrary to Tregneza’s method described in “Analysing sky luminance scans to obtain frequency distributions of CIE Standard General Skies“, the luminance distribution is normalized with the zenith luminance.

Usage:

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

Where:

ParameterDescription
skyReturns the best fitting CIE standard general sky as in CIE S 011, determined with Tregenza method.
RMSReturns the Root Mean Square deviation from the best fitting CIE standard general sky.
LDefines the Tregenza hemisphere luminance distribution.
sunazDefines the sun azimuth angle \alpha_S.
sunelDefines the sun elevation angle \gamma_S.
mode
(optional)
Defines the luminance determination mode of the reference data:
’center’ default: uses the patch center point angles for luminance determination.
’mean’ uses the mean luminance of the four patch corner luminances as
suggested by Tregenza.

Examples

Determine CIE skytype at \alpha_S = 166\degree and \gamma_S = 33\degree:

L = ciesky(12,166,33);
[sky,RMS] = tregenzaskytype(L,166,33)

See also: ciesky

Result:

sky = 12
RMS = 0

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

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

See also: ciesky

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’.

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).

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