转自：
http://www.cnblogs.com/gis_gps/archive/2009/02/12/1389071.html
备用
一、背景:
如何判断一个指定的经纬度点是否落在一个多边形区域内？
二、实现代码(delphi)
Type
TMyPoint =
packed
record
X : double;
Y : double;
end;
{*------------------------------------------------------------------------------
判断指定的经纬度坐标点是否落在指定的多边形区域内
@param ALon 指定点的经度
@param ALat 指定点的纬度
@param APoints 指定多边形区域各个节点坐标
@return True 落在范围内 False 不在范围内
------------------------------------------------------------------------------*}
function IsPtInPoly(ALon, ALat: double; APoints:
array
of TMyPoint): Boolean;
var
iSum, iCount, iIndex: Integer;
dLon1, dLon2, dLat1, dLat2, dLon: double;
begin
Result := False;
if (Length(APoints)
<
3)
then
begin
Result := False;
Exit;
end;
iSum :=
0;
iCount := Length(APoints);
for iIndex :=0
to iCount
-
1
do
begin
if (iIndex
= iCount
-
1)
then
begin
dLon1 := APoints[iIndex].X;
dLat1 := APoints[iIndex].Y;
dLon2 := APoints[0].X;
dLat2 := APoints[0].Y;
end
else
begin
dLon1 := APoints[iIndex].X;
dLat1 := APoints[iIndex].Y;
dLon2 := APoints[iIndex
+
1].X;
dLat2 := APoints[iIndex
+
1].Y;
end;
if ((ALat
>= dLat1)
and (ALat
< dLat2))
or ((ALat>=dLat2)
and (ALat
< dLat1))
then
begin
if (abs(dLat1
- dLat2)
>
0)
then
begin
dLon := dLon1
- ((dLon1
-dLon2)
* (dLat1
-ALat))
/ (dLat1
- dLat2);
if (dLon
< ALon)
then
Inc(iSum);
end;
end;
end;
if (iSum
mod
2
<>
0)
then
Result := True;
end;
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C#算法：