AutoCAD VBA二次开发(4)

 应用VBA程序绘制样条曲线的方法为：AddSpline(PointsArray, StartTangent, EndTangent)，其中，PointsArray为样条曲线（渐开线）拟合点的3维坐标组成的列表（即数组，必须为3的倍数），StartTangent，EndTangent为样条曲线的起点和终点切向向量（必需为3元素列表，切向必需与曲线的走向一致）^[8]。起点的切向竖直向上^[7]181-183，可取(0, 1, 0)；根据式(2)可知终点的切向为。

可根据精度要求将所绘渐开线的展角上限等分为J个区间（程序中取J=10），应用For…Next循环计算拟合点的坐标。首先按下式计算展角：

， (j=0, 1, 2, …, J)                                    (3)

再用式(1)计算点K的坐标(x_Kj, y_Kj)。

图18  绘制渐开线的窗体

绘制渐开线及基圆的窗体如图18所示，程序如下：

Private Sub cmdOK_Click()

  ThisDrawing.Application.Documents.Add

  pi = 4 * Atn(1)                   ’ 定义常数π

  Dim rb As Double                ’ 定义基圆半径

  Dim theta0 As Double             ’ 定义渐开线展角

  Dim InvPoint(0 To 32) As Double    ’ 定义拟合点坐标

  Dim SPtan(0 To 2) As Double       ’ 定义起点切线方向

  Dim EPtan(0 To 2) As Double       ’ 定义终点切线方向

  Dim InvObj As AcadSpline         ’ 定义Spline对象

  rb = txtRb.Text

  theta0 = txtTheta0.Text * pi / 180     ’ 将角度转换为弧度

  delta_theta = theta0 / 10

  For j = 0 To 10

     theta = j * delta_theta

     InvPoint(j * 3) = rb * (Sin(theta) - theta * Cos(theta))

     InvPoint(j * 3 + 1) = rb * (Cos(theta) + theta * Sin(theta))

     InvPoint(j * 3 + 2) = 0

  Next j

  SPtan(0) = 0: SPtan(1) = 1: SPtan(2) = 0

  EPtan(0) = 1: EPtan(1) = 1 / Tan(theta0): EPtan(2) = 0

  ’ 设置Spline对象

  Set InvObj = ThisDrawing.ModelSpace.AddSpline(InvPoint, SPtan, EPtan)

 

  ’ 绘制基圆

  Dim CirObj As AcadCircle       ’ 定义Circle对象

  Dim CenPoint(0 To 2) As Double  ’ 定义圆心坐标

  CenPoint(0) = 0: CenPoint(1) = 0: CenPoint(2) = 0

  ’ 设置Circle对象

  Set CirObj = ThisDrawing.ModelSpace.AddCircle(CenPoint, rb)

  ThisDrawing.SaveAs (“D:\Draw_Inv.dwg”)

End Sub