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We use R-functions to represent a CSG object by a single real function. Well-known min/max functions are only C0 continuous. This can cause unpredictable results in further operations on the object. Other R-functions can provide C1 and even Ck continuity of the resulting function. It helped to formulate analytical descriptions for such operations as blending, offsetting, sweeping and others.

Click to get a more large image of a CSG chair

Details on set-theoretic and many other operations with R-functions can be found in the paper:

Pasko A.A., Adzhiev V.D., Sourin A.I., Savchenko V.V. “Function representation in geometric modeling: concepts, implementation and applications”, The Visual Computer, vol.11, No.8, 1995, pp.429-446.
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