[求助]：已知二点和半径，怎么画圆??

arja

能不能请斑主写一个lisp程序出来呢？

dbzdbz

可不可以把那两点看成是切点，然后用相切相切半径画圆？？？

maplesu

点是切点，那切线是什么呢？
你要是用相切捕捉根本就捕捉不到点的！

alldesign

二楼的方法不错

informore

看来还是没有什么简洁的办法....
郁闷

虾仔

已知两点和半径理论上是有两个解的，如果两点刚好是在直径上则只有一个解，所以应该还要有圆心方向

xiaotang

提供一种绘图思路：三点画圆
假设有AB两点，先做过A点的垂线，然后以B点为圆心，2r为半径画圆，与过A点的垂线相交两点，然后分别过这两点，利用三点画圆，可做出过AB的两个圆，满足题目要求。

kkhhdd

嗯.我发觉二楼的方法不错..... 但是１３楼有道理

自由的鱼

根据2楼的思路，写了这个程序，圆方向无法判断，所以生成两个圆，不要的圆楼主就手工删除掉，：）

Option Explicit

Sub addcircle()
Dim rads As Double
Dim intpnts As Variant
rads = InputBox("输入圆半径")
Dim sset As AcadSelectionSet
Dim circleobj(1) As AcadCircle
Dim p1(0 To 2) As Double
Dim p2(0 To 2) As Double
Dim i As Integer
Set sset = ThisDrawing.SelectionSets.Add("c1c")
sset.SelectOnScreen


For i = 0 To 1
Set circleobj(i) = ThisDrawing.ModelSpace.addcircle(sset.Item(i).Coordinates, rads)

Next
intpnts = circleobj(0).IntersectWith(circleobj(1), acExtendNone)
circleobj(0).Delete
circleobj(1).Delete


p1(0) = intpnts(0): p1(1) = intpnts(1): p1(2) = intpnts(2)

p2(0) = intpnts(3): p2(1) = intpnts(4): p2(2) = intpnts(5)
Set circleobj(0) = ThisDrawing.ModelSpace.addcircle(p1, rads)

Set circleobj(1) = ThisDrawing.ModelSpace.addcircle(p2, rads)
sset.Delete
End Sub

maplesu

我也来写一个lisp
可以选择方向！

[PHP]
(defun c:c2()
  (setq pt1 (getpoint "第一点： ")
        pt2 (getpoint "第二点： ")
        r (getreal "半径： ")
        pt3 (getpoint "方向： "))
  (setq os (getvar "osmode"))
  (setvar "osmode" 0)
  (setq a (angle pt1 pt2)
        d (distance pt1 pt2)
        dd (/ d 2)
        ll (sqrt (- (* r r) (* dd dd)))       
        a2 (atan ll dd)
        a1 (angle pt1 pt3)
        )  
  (if (<= a pi)
    (progn
      (if (and (> a1 a) (< a1 (+ a pi)))
        (setq aa (+ a a2))
        (setq aa (- a a2))))
    (progn
      (if (and (< a1 a) (> a1 (- a pi)))
        (setq aa (- a a2))
        (setq aa (+ a a2))))
    )
  (setq pc (polar pt1 aa r))
  (command "CIRCLE" pc r)
  (setvar "osmode" os)
  )
[/PHP]

自由的鱼

加了选择方向功能，用的是笨办法，呵呵

Option Explicit

Sub addcircle()
On Error Resume Next
Dim rads As Double
Dim intpnts As Variant
rads = InputBox("输入圆半径")
Dim sset As AcadSelectionSet
Dim circleobj(1) As AcadCircle
Dim p1(0 To 2) As Double
Dim p2(0 To 2) As Double
Dim i As Integer
Dim fxd As Variant
Dim Lobj As AcadLine
Dim Tobj As AcadLine
Dim TMP As Variant
Set sset = ThisDrawing.SelectionSets.Add("c112c")
sset.SelectOnScreen
fxd = ThisDrawing.Utility.GetPoint(, "请选择方向点")
For i = 0 To 1
    Set circleobj(i) = ThisDrawing.ModelSpace.addcircle(sset.Item(i).Coordinates, rads)
Next
intpnts = circleobj(0).IntersectWith(circleobj(1), acExtendNone)
circleobj(0).Delete
circleobj(1).Delete
p1(0) = intpnts(0): p1(1) = intpnts(1): p1(2) = intpnts(2)
p2(0) = intpnts(3): p2(1) = intpnts(4): p2(2) = intpnts(5)
Set Tobj = ThisDrawing.ModelSpace.AddLine(fxd, p1)
Set Lobj = ThisDrawing.ModelSpace.AddLine(p1, p2)
TMP = Tobj.IntersectWith(Lobj, acExtendNone)
If UBound(TMP) = 0 Then
    Set circleobj(0) = ThisDrawing.ModelSpace.addcircle(p2, rads)
Else
    Set circleobj(1) = ThisDrawing.ModelSpace.addcircle(p1, rads)
End If
Tobj.Delete
Lobj.Delete
sset.Delete
End Sub