How does Sketchpoint work?

[albie0803]

I'm trying to dimension between the centres of the 2 arcs of a keyway sketch

210 S.AddLine(LS1X, LS1Y, LE1X, LE1Y, False)
211 S.AddLine(LS2X, LS2Y, LE2X, LE2Y, False)
212
213 ARC1 = S.AddArcCenterStartEnd(ERC1, 0.0, ERC1, ER, ERC1, -ER, False)
214 S.AddDimension(ARC1)
215 ARC2 = S.AddArcCenterStartEnd(ERC2, 0.0, ERC2, -ER, ERC2, ER, False)
216 S.AddDimension(ARC2)
217
218 P1 = SketchPoint(ERC1, 0, True)
219 P2 = SketchPoint(ERC2, 0, True)
220 S.AddDimension(P1, P2)

P1 = SketchPoint(ERC1, 0, True) gives me Object reference not set to an instance of an object at line 220

P1 = S.SketchPoint(ERC1, 0, True) gives me AttributeError: 'Sketch' object has no attribute 'SketchPoint' at line 218