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Kennelly, J., & Stewart, J. (2006). A Uniform Sky Illumination Model to Enhance Shading of Terrain and Urban Areas. Cartography and Geographic Information Science, 33(1), 21–36. https://doi.org/10.1559/152304006777323118.
Jenny, Bernhard; Hurni, Lorenz (2006). "Swiss-Style Colour Relief Shading Modulated by Elevation and by Exposure to Illumination". The Cartographic Journal. 43 (3): 198–207. Bibcode:2006CartJ..43..198J. doi:10.1179/000870406X158164.