新手求教，请大神给注释一下下面的代码?

耕居琅琊郡

Public Function CreateUCS3Point(ByVal originWcs As Variant, ByVal xAxisPointWcs As Variant, ByVal yAxisPointWcs As Variant, _
    ucsName As String, ByRef objUCS As AcadUCS) As Boolean
    ' 如果pt1和pt2重合
    Dim math As New clsMath
    If math.PointIsEqual(originWcs, xAxisPointWcs) Then
        CreateUCS3Point = False
    End If

    Dim a1 As Double, b1 As Double, c1 As Double
    Dim a2 As Double, b2 As Double, c2 As Double
    Dim x As Double, y As Double, z As Double
    y = (yAxisPointWcs(1) + xAxisPointWcs(1)) / 2

    a1 = xAxisPointWcs(0) - originWcs(0) '
    b1 = xAxisPointWcs(2) - originWcs(2)
    c1 = (originWcs(1) - xAxisPointWcs(1)) * y

    a2 = ((xAxisPointWcs(1) - originWcs(1)) * (yAxisPointWcs(2) - originWcs(2))) - ((yAxisPointWcs(1) - originWcs(1)) * (xAxisPointWcs(2) - originWcs(2)))
    b2 = (a1 * (yAxisPointWcs(1) - originWcs(1))) - ((xAxisPointWcs(1) - originWcs(1)) * (yAxisPointWcs(0) - originWcs(0)))
    c2 = (a1 * (yAxisPointWcs(2) - originWcs(2)) - b1 * (yAxisPointWcs(0) - originWcs(0))) * y

    ' 如果三点共线或重合
    If (a1 * b2 - a2 * b1) = 0 Then
        CreateUCS3Point = False
    Else

    x = (c1 * b2 - c2 * b1) / (a1 * b2 - a2 * b1)

    z = (c2 * a1 - c1 * a2) / (a1 * b2 - a2 * b1)

    ' 将假定的偏移量加在坐标上
    Dim ptY(0 To 2) As Double
    SetPoint3d ptY, x + originWcs(0), y + originWcs(1), z + originWcs(2)

    Set objUCS = ThisDrawing.UserCoordinateSystems.Add(originWcs, xAxisPointWcs, ptY, ucsName)
    CreateUCS3Point = True
    End If
End Function

耕居琅琊郡

实在是看不懂这段代码了，尤其是判断三点共线或重合这段。
请大侠指点，谢谢

zzyong00

耕居琅琊郡 发表于 2016-6-20 11:32
实在是看不懂这段代码了，尤其是判断三点共线或重合这段。
请大侠指点，谢谢

三点共线，用向量叉积为0，这是高等数学的事儿
数学，对于编程来说很重要

zzyong00

去本论坛里的“几何算法”学习学习吧

Zzllvb

是的，是判断三点共线的，向量这个工具很有用