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When you render curves, you may be interested in the following attributes and options.
Within the PrmanObjectStatements node, within the Advanced layout, there is an option to tell RenderMan to render curves as "roundcurves". Otherwise, you will render the curves as flat ribbons. If you are rendering hair, especially long hair, we recommend that you turn the "hair" attribute shown below to "Yes".
Within the PrmanGlobalStatements node, in the Advanced layout, there are a few more options you may be interested in. You can find them within the options -> dice and options -> hair section of the parameters.