NURBS can be open or closed. When closed, the minimum and maximum boundaries are joined by segments or patches.
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| Open curve
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Closed curve
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A surface can be open in both U and V like a grid, closed in both like a torus, or open in one and closed in the other like
a tube.
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| Open in U and V.
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Open in U, closed in V.
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| Closed in U, open in V.
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Closed in U and V.
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