frudawski

polardataCCT

The polardataCCT function calculates the resulting horizontal and vertical Correlated Colour Temperatures (CCTs) T_{cp,i} from the Tregenza radiance distribution with 145 patches and the colour coordinates x and y.

Usage:

[Th,Tv] = polardataCCT(x,y,L,vdir,omega,method)

Where:

ParameterDescription
ThIs the resulting horizontal integral CCT T_{cp,h}.
TvAre the resulting vertical integral CCT T_{cp,v,i} in i vertical directions, specified by the vdir parameter. Note: this method neglects the influence of the sourrounding reflectances e.g. the environment terrain.
x,yAre the Tregenza patches CIE 1931 colour coordinates x and y as 145 \times 1 vector.
LIs the Tregenza luminance distribution in \textrm{cd}\cdot\textrm{m}^2 as 145 \times 1 vector.
vdir
(optional)
Specifies the vertical compass direction using the azimuth angle, starting in north and going clockwise, default [0:359]. For compass directions north, east, south, west use: [0 90 180 270]
omega
(optional)
Defines the patches solid angles in \mathrm{sr} as 145 \times 1 vector. Default value: 9.6° \approx 0.022~\mathrm{sr}.
method
(optional)
Defines the CCT determination method:
‘Robertson’ (default)
‘exact’

See also: ciexy2cct

Examples

Horizontal and vertical resulting CCT (N,E,S,W) for CIE sky 12 with \alpha_S=166° and \gamma_S = 33°:

x = linspace(0.2,0.4,145);
y = linspace(0.4,0.3,145);
Y = ciesky(12,166,33);
[Th,Tv] = polardataCCT(x,y,Y,[0 90 180 270])

See also: ciesky

Result:

Th = 6109
Tv =

   8412
   8052
   8028
   8285

Horizontal and vertical resulting CCT for \alpha = 0°, 30°, 60°, 90°, 120°, 150°, 180° for CIE sky 5 with \alpha_S=180° and \gamma_S = 30°, \omega = 12° = 0.03442~\textrm{sr} and method = ‘exact’:

x = linspace(0.2,0.4,145);
y = linspace(0.4,0.3,145);
Y = ciesky(5,180,30);
omega = ones(1,145).*0.03442;
[Th,Tv] = polardataCCT(x,y,Y,[0 30 60 90 120 150 180],omega,'exact')

See also: ciesky

Result:

Th = 5328
Tv =

   7476.9
   7477.8
   7460.7
   7459.8
   7450.7
   7466.0
   7471.2

Reference

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).

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