Use arc x1,y1..x4,y4 points to extract arc start and sweep angles.
protected Void CalcArcAngles(Int32 X1,
     Int32 Y1,
     Int32 X2,
     Int32 Y2,
     Int32 X3,
     Int32 Y3,
     Int32 X4,
     Int32 Y4,
     Double& startangle,
     Double& sweepangle)

See Also

Graphics3D Class | Graphics3D Members | Steema.TeeChart.Drawing Namespace