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Auto – It uses the Viewport UV set name to set the material attribute.
From ImageFile – Sets the name of the UV material attribute the same as the UV texture attribute. However, UV changes will are not be shown in the viewport.
Manual – This option allows manual setting of the viewport UV attribute for all materials. It is recommended to switch first to From ImageFile, then to Manual, as the default option is Auto - which means V-Ray automatically assigns UV attribute name.
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