Sky luminance: Standard digital form for modelling

Roy, Geoffrey G.; Ruck, Nancy C.; Reid, Graham; Julian, Warren G.

doi:10.1177/14771535950270030501

Cited by 2 publications

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“…Once a 'clean' image has been created it is then possible to undertake further analysis to provide a concise way of describing where the clouds are and to compute the cloud coverage over the whole sky on designated regions of the sky dome. Drawing upon the Standard Data Format (SDF) technique, 11 clouds are represented by sets of polylines describing the outer edge of each cloud patch as a set of vectors across the sky dome. This offers an efficient way of describing the complex boundary conditions, including clouds with 'sky holes'.…”

Section: Cloud Outliningmentioning

confidence: 99%

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Sky analysis from CCD images: cloud cover

Roy

Hayman²,

Julian

2001

Lighting Research & Technology

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One of the tasks in sky modelling is the determination of the location and amount of cloud coverage in the sky. Analysis using digital camera systems is possible but requires an automated method of separating sky images into clear sky and cloud regions. Two segmentation approaches have been used in this research, one based purely upon the colour characteristics of sky regions, the other a neural network approach using a wider range of variables. A convolution technique was developed to reduce classification errors prior to defining cloud outlines using polylines. Sensitivity analysis shows that this can be carried out efficiently with little loss of accuracy.

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Section: Cloud Outliningmentioning

confidence: 99%

“…Once the outlines of the clouds are known we can compute the area of each polygon shape (on the sky dome) using the functions from the SDF 11 modelling package, see Roy et al 13 Summing these for each cloud patch gives the estimated total cloud coverage.…”

Section: Cloud Outliningmentioning

confidence: 99%

Sky analysis from CCD images: cloud cover

Roy

Hayman²,

Julian

2001

Lighting Research & Technology

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Measurement of the All Sky Spectral Radiance Distribution Using a Digital Camera With a Fisheye Lens

Yatsuzuka¹,

Uetani²

2013

Nihon Kenchiku Gakkai Kankyokei Ronbunshu

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We developed a method of measuring the spectral radiance of all sky elements using a general purpose digital camera and a circular fisheye lens. The accuracy of the fisheye camera is adequate for practical daylight design. The instrument is portable for field measurements. The digital camera with the fisheye lens is colorimetrically calibrated to obtain the calibration functions which transfer the video signal values RGB on a digital color image into the absolute values of CIE 1931 tristimulus values XYZ pixel by pixel. The calibrated fisheye digital camera measures the all sky distribution of the XYZ tristimulus values. The XYZ tristimulus values are transferred into the all sky spectral radiance distribution in two ways: (1) by using the CIE daylight illuminant and (2) by using the eigenvectors obtained by principal component analysis of measured spectral radiances of the sky elements by a spectroradiometer. The accuracy of the all sky spectral radiance distribution is validated by comparison with the spectral radiance measured by the spectroradiometer.

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Sky luminance: Standard digital form for modelling

Cited by 2 publications

References 0 publications

Sky analysis from CCD images: cloud cover

Sky analysis from CCD images: cloud cover

Measurement of the All Sky Spectral Radiance Distribution Using a Digital Camera With a Fisheye Lens

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