frudawski

polardataE

The polardataE function calculates the resulting horizontal and vertical illuminances for a given Tregenza luminance distribution with 145 patches. The Tregenza hemisphere is assumed to have 100% coverage as in figure 1 in contrast to the original Tregenza model.

Figure 1: Tregenza hemisphere with 100% coverage

Usage:

Plain text
Copy to clipboard
Open code in new window
EnlighterJS 3 Syntax Highlighter
[Eh,Ev] = polardataE(L,vdir)
[Eh,Ev] = polardataE(L,vdir)
[Eh,Ev] = polardataE(L,vdir)

Where:

ParameterDescription
EhIs the resulting horizontal illuminance EhE_h.
EvAre the resulting vertical illuminances Ev,iE_{v,i} in ii vertical directions, specified by the vdir parameter. Note: this method neglects the influence of the sourrounding reflectances e.g. the environment terrain.
LIs the Tregenza luminance distribution in cdm2\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]

Examples

Horizontal and vertical illuminance (N,E,S,W) for CIE sky 5 with αS=180°\alpha_S=180° and γS=40°\gamma_S = 40°:

Plain text
Copy to clipboard
Open code in new window
EnlighterJS 3 Syntax Highlighter
L = ciesky(5,180,40,'Eh',10000);
[Eh,Ev] = polardataE(L,[0 90 180 270])
L = ciesky(5,180,40,'Eh',10000); [Eh,Ev] = polardataE(L,[0 90 180 270])
L = ciesky(5,180,40,'Eh',10000);
[Eh,Ev] = polardataE(L,[0 90 180 270])

See also: ciesky

Result:

Plain text
Copy to clipboard
Open code in new window
EnlighterJS 3 Syntax Highlighter
Eh = 10000.0
Ev =
4896.3
4904.7
4900.4
4896.6
Eh = 10000.0 Ev = 4896.3 4904.7 4900.4 4896.6
Eh = 10000.0
Ev =

   4896.3
   4904.7
   4900.4
   4896.6

Note: CIE sky 5 has a uniform luminance distribution. The differences in the resulting vertical illuminances are due to different patch center coordinates which are used for cosine correction of the individual patch.

Vertical illuminance for α=160°\alpha = 160° for CIE sky 12 with αS=160°\alpha_S=160° and γS=40°\gamma_S = 40°:

Plain text
Copy to clipboard
Open code in new window
EnlighterJS 3 Syntax Highlighter
L = ciesky(12,160,40,'Eh',50000);
[~,Ev] = polardataE(L,160)
L = ciesky(12,160,40,'Eh',50000); [~,Ev] = polardataE(L,160)
L = ciesky(12,160,40,'Eh',50000);
[~,Ev] = polardataE(L,160)

See also: ciesky

Result:

Plain text
Copy to clipboard
Open code in new window
EnlighterJS 3 Syntax Highlighter
Ev = 5.0554e+04
Ev = 5.0554e+04
Ev = 5.0554e+04

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).

Leave a comment

* I accept the use of cookies as well as the terms in the privacy policy. I accept that data provided by me is processed and saved. I know and accept that comments may be saved and published after review.