用VBA编程，画一条曲线，如用三个点，怎么画？

Sub Test()
       Dim pt1 As Variant
       Dim pt2 As Variant
       Dim pt3 As Variant
       pt1 = ThisDrawing.Utility.GetPoint(, "指定圆弧的起点: ")
       pt2 = ThisDrawing.Utility.GetPoint(, "指定圆弧的第二个点: ")
       pt3 = ThisDrawing.Utility.GetPoint(, "指定圆弧的端点:: ")
       Const PI = 3.1415926
       ' 第一段角度
       Dim ang As Double
       ang = ThisDrawing.Utility.AngleFromXAxis(pt1, pt2)
         ' 第一段中点
       Dim spt(0 To 2) As Double
       spt(0) = (pt1(0) + pt2(0)) / 2
       spt(1) = (pt1(1) + pt2(1)) / 2
       Dim ept As Variant
       ept = ThisDrawing.Utility.PolarPoint(spt, ang - PI / 2, 1000)
       ' 第一段垂直平分线
       Dim LineObj1 As AcadLine
       Set LineObj1 = ThisDrawing.ModelSpace.AddLine(spt, ept)
       ' 第二段角度
       ang = ThisDrawing.Utility.AngleFromXAxis(pt3, pt2)
       ' 第二段中点
       spt(0) = (pt3(0) + pt2(0)) / 2
       spt(1) = (pt3(1) + pt2(1)) / 2
       ept = ThisDrawing.Utility.PolarPoint(spt, ang + PI / 2, 1000)
       ' 第二段垂直平分线
       Dim LineObj2 As AcadLine
       Set LineObj2 = ThisDrawing.ModelSpace.AddLine(spt, ept)
       ' 求交点，即为圆心
       Dim cpt As Variant
       cpt = LineObj1.IntersectWith(LineObj2, acExtendBoth)
       LineObj1.Delete
       LineObj2.Delete
       ' 求圆心与端点的距离，即为半径
       Dim r As Double
       r = Sqr((cpt(0) - pt1(0)) ^ 2 + (cpt(1) - pt1(1)) ^ 2)
       ' 求起始角度和终止角度
       Dim sang As Double
       sang = ThisDrawing.Utility.AngleFromXAxis(cpt, pt1)
       Dim eang As Double
       eang = ThisDrawing.Utility.AngleFromXAxis(cpt, pt3)
       If sang > eang Then
               sang = ThisDrawing.Utility.AngleFromXAxis(cpt, pt3)
               eang = ThisDrawing.Utility.AngleFromXAxis(cpt, pt1)
       End If
       ThisDrawing.ModelSpace.AddArc cpt, r, sang, eang
End Sub