In CityEngine, if we have two roads structured as two concentric circles, the block generated by the inner circle will be completely covered by the outer one (as is shown in picture below, though it's not circle, but the situation is just alike) when there's no outer circle, the block generated is like this: and when the shape of outer block is formed, the inner block cannot be chosen any more. I think it's like an island, and the proper topology should be like only the region (or block) between two circles is formed, and the region inside the inner circle is cut out. Is there a way to make this possible?
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