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What is it? The hemisphere environment mode in iray basically creates a hemispherical dome where the bottom is squished and uses the HDR like a texture map. Instead of using the default infinite environment you can enable this mode and give the illusion of your geometry in the HDR. It’s a neat looking ‘trick’ and especially cool when used in combination with the iray active shade mode.
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http://jeffpatton.net/2011/12/iray-hemi ... ment-mode/
