كود :
'Find a circle through the three points.
Private Sub FindCircle(ByVal a As PointF, ByVal b As PointF, ByVal c As PointF, ByRef center As PointF, ByRef radius As Single)
' Get the perpendicular bisector of (x1, y1) and (x2, y2).
Dim x1 As Single = (b.X + a.X) / 2
Dim y1 As Single = (b.Y + a.Y) / 2
Dim dy1 As Single = b.X - a.X
Dim dx1 As Single = -(b.Y - a.Y)
' Get the perpendicular bisector of (x2, y2) and (x3, y3).
Dim x2 As Single = (c.X + b.X) / 2
Dim y2 As Single = (c.Y + b.Y) / 2
Dim dy2 As Single = c.X - b.X
Dim dx2 As Single = -(c.Y - b.Y)
' See where the lines intersect.
Dim lines_intersect, segments_intersect As Boolean
Dim intersection, close1, close2 As PointF
FindIntersection(New PointF(x1, y1), New PointF(x1 + dx1, y1 + dy1), New PointF(x2, y2), New PointF(x2 + dx2, y2 + dy2), lines_intersect, segments_intersect, intersection, close1, close2)
If Not lines_intersect Then
MessageBox.Show("The points are colinear")
center = New PointF(0, 0)
radius = 0
Else
center = intersection
Dim dx As Single = center.X - a.X
Dim dy As Single = center.Y - a.Y
radius = CSng(Math.Sqrt(dx * dx + dy * dy))
End If
End Sub
' Find the point of intersection between the lines p1 --> p2 and p3 --> p4.
Private Sub FindIntersection(ByVal p1 As PointF, ByVal p2 As PointF, ByVal p3 As PointF, ByVal p4 As PointF, ByRef lines_intersect As Boolean, ByRef segments_intersect As Boolean, ByRef intersection As PointF, ByRef close_p1 As PointF, ByRef close_p2 As PointF)
' Get the segments' parameters.
Dim dx12 As Single = p2.X - p1.X
Dim dy12 As Single = p2.Y - p1.Y
Dim dx34 As Single = p4.X - p3.X
Dim dy34 As Single = p4.Y - p3.Y
' Solve for t1 and t2
Dim denominator As Single = (dy12 * dx34 - dx12 * dy34)
Dim t1 As Single = ((p1.X - p3.X) * dy34 + (p3.Y - p1.Y) * dx34) / denominator
If Single.IsInfinity(t1) Then
' The lines are parallel (or close enough to it).
lines_intersect = False
segments_intersect = False
intersection = New PointF(Single.NaN, Single.NaN)
close_p1 = New PointF(Single.NaN, Single.NaN)
close_p2 = New PointF(Single.NaN, Single.NaN)
Return
End If
lines_intersect = True
Dim t2 As Single = ((p3.X - p1.X) * dy12 + (p1.Y - p3.Y) * dx12) / -denominator
' Find the point of intersection.
intersection = New PointF(p1.X + dx12 * t1, p1.Y + dy12 * t1)
' The segments intersect if t1 and t2 are between 0 and 1.
segments_intersect = ((t1 >= 0) AndAlso (t1 <= 1) AndAlso (t2 >= 0) AndAlso (t2 <= 1))
' Find the closest points on the segments.
If t1 < 0 Then
t1 = 0
ElseIf t1 > 1 Then
t1 = 1
End If
If t2 < 0 Then
t2 = 0
ElseIf t2 > 1 Then
t2 = 1
End If
close_p1 = New PointF(p1.X + dx12 * t1, p1.Y + dy12 * t1)
close_p2 = New PointF(p3.X + dx34 * t2, p3.Y + dy34 * t2)
End Sub