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The points returned in the sequence they were created. It is all up to you to sort them. You can use the SketchSegment::ConstructionGeometry to filter the centerlines. In regard to arc properties you can convert ISketchSegment to ISketchArc (just cast it) and you can find the methods like SketchArc::GetCenterPoint2 which returns the center point of the arc. You can also get the end points to calculate virtual sharp.
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