private function getcenof3pt(pt1 as variant, pt2 as variant, pt3 as variant, byref radius as double) as variant
''''根據三點計算出圓心和半徑
dim xysm, xyse, xy as double
dim ptcen(2) as double
xy = pt1(0) ^ 2 + pt1(1) ^ 2
xyse = xy - pt3(0) ^ 2 - pt3(1) ^ 2
xysm = xy - pt2(0) ^ 2 - pt2(1) ^ 2
xy = (pt1(0) - pt2(0)) * (pt1(1) - pt3(1)) - (pt1(0) - pt3(0)) * (pt1(1) - pt2(1))
'''判斷引數有效性
if abs(xy) < 0.000001 then
msgbox "所輸入的引數無法建立圓形！"
exit function
end if
'獲得圓心和半徑
ptcen(0) = (xysm * (pt1(1) - pt3(1)) - xyse * (pt1(1) - pt2(1))) / (2 * xy)
ptcen(1) = (xyse * (pt1(0) - pt2(0)) - xysm * (pt1(0) - pt3(0))) / (2 * xy)
ptcen(2) = 0
radius = sqr((pt1(0) - ptcen(0)) * (pt1(0) - ptcen(0)) + (pt1(1) - ptcen(1)) * (pt1(1) - ptcen(1)))
if radius < 0.000001 then
msgbox "半徑過小！"
exit function
end if
''函式返回圓心的位置，而半徑則在引數中通過引用方式返回
getcenof3pt = ptcen
end function
public function addarc3pt(byval ptst as variant, byval ptsc as variant, byval pten as variant) as acadarc
''''三點法建立圓弧
dim objarc as acadarc
dim ptcen as variant
dim radius as double
ptcen = getcenof3pt(ptst, ptsc, pten, radius)
if isclockwise(ptcen, ptst, ptsc, pten) then
set objarc = addarccsep(ptcen, ptst, pten)
else
set objarc = addarccsep(ptcen, pten, ptst)
end if
objarc.update
set addarc3pt = objarc
end function
private function addarccsep(byval ptcen as variant, byval ptst as variant, byval pten as variant) as acadarc
dim objarc as acadarc
dim radius as double
dim stang, enang as double
''計算半徑
radius = getdistance(ptcen, ptst)
''計算起點角度和終點角度
stang = thisdrawing.utility.anglefromxaxis(ptcen, ptst)
enang = thisdrawing.utility.anglefromxaxis(ptcen, pten)
set objarc = thisdrawing.modelspace.addarc(ptcen, radius, stang, enang)
objarc.update
set addarccsep = objarc
end function
'判斷三點的方向
function isclockwise(ptcen, ptst, ptsc, pten) as boolean
a1 = thisdrawing.utility.anglefromxaxis(ptcen, ptst)
a2 = thisdrawing.utility.anglefromxaxis(ptcen, ptsc)
a3 = thisdrawing.utility.anglefromxaxis(ptcen, pten)
isclockwise = (a1 < a2) xor (a2 < a3) xor (a1 < a3)
end function
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