Characterization of sky scanner measurements based on CIE and ISO standard CIE S 011/2003

Abstract

The aim of this paper is to present a complete analysis of the sky luminance distribution data measured with a sky scanner at the International Daylight Measurement Program station in Lyon. Besides presentation of the sky luminance distribution, we also derive the CIE sky type based on the CIE S 011/2003 standard. The CIE sky type is based on gradation and indicatrix functions. Determination of the gradation and indicatrix group is based on the calculation of luminance ratio between two elements on every almucantar. Since there are six gradation and six indicatrix groups, we have 36 combinations but only 15 of them are listed in the CIE standard. Since some of combinations are really rare, we provide a table to show how to allocate 36 combinations to 15 standard CIE sky types. At the end of the paper, we present frequencies of occurrence of CIE sky types in Lyon.

Evaluation of Two Procedures for Selecting the CIE Standard Sky Type Using High Dynamic Range Images

“…This procedure, described by Kobav et al (2012) and adapted by Souza et al (2016), is aimed at determining the gradation and indicatrix sky functions. The CIE standard results from the combination of the obtained gradation and indicatrix functions.…”

A Practical Device for Measuring the Luminance Distribution

“…The actual time necessary to take the LDR images was the time that the device was vulnerable to transient conditions. This was approximately 8 s, compared to 3 min required for a sky scanner [32][33][34], and 1-2 min for HDR camera system measurement [8].…”

Classifying skies from images: A multidimensional approach to detecting high dynamic range imaging attributes

“…In this routine, the normalised luminance L 90 was taken from the pixels at the intersection of the 188 almucantar and the 908 angular distance, in order to provide an optimal relation between the lowest unobstructed sky and the solar altitude. 29 Figure 3 shows an example of the functions collected from the HDR image, compared to the CIE groups. The scanned pixels are then compared to the original CIE equations using the root mean squared error (RMSE) and then analysed with a conversion table 29 to fit the results in the 15 CIE sky types.…”

“…29 Figure 3 shows an example of the functions collected from the HDR image, compared to the CIE groups. The scanned pixels are then compared to the original CIE equations using the root mean squared error (RMSE) and then analysed with a conversion table 29 to fit the results in the 15 CIE sky types. Since this method uses the position of the sun as reference, there are two possible reading directions for each function, clockwise (positive) and counter-clockwise (negative), thus creating four different relations: ' P f P , ' N f N , ' P f N and ' N f P .…”