maxHoleGap: specifies the maximum number of degrees of arc that can be missing from an extracted hole’s wall. Holes with missing wall portions can sometimes be created with drilling, and so are sometimes recognized as hole GCDs. But if more than this amount is missing, no hole GCD is recognized, and a curved wall GCD is extracted instead. The default maximum hole gap is 180 degrees. In other words, if no more than half of the wall is missing, a hole GCD is recognized by default.