shp.AddPart(_polygon, CoordinateType.Regular);
f = new Feature(shp); //Feature 类型的f
IGeometry ig = getGeomFromRow(sourceDt.Rows[0]);
f = f.Difference(ig);
f,与ig都是没有问题的,执行f=f.Difference(ig)时,出现no outgoing dirEdge found [ DotSpatial.Topology.Coordinate ]
Difference到底怎么用