Determine if a point falls within the polygon

Turn from: http://www.cnblogs.com/gis_gps/archive/2009/02/12/1389071.html

Spare

I. Background:

How to determine whether a specified latitude and longitude point falls in a polygon region.

Second, the Implementation Code (Delphi)

Type
Tmypoint = Packed record
x:double;
y:double;
End

{*------------------------------------------------------------------------------
Determines whether the specified latitude and longitude coordinate point falls within the specified polygon region
@param the longitude of the ALon point
@param the latitude of the Alat point
@param apoints Specifies the coordinates of each node of the polygon region
@return True falls within range False is not in range
------------------------------------------------------------------------------*}
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&GT;=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

_______________________________________________________________________________________________________________ _____________

C # algorithm:///<summary>        ///  Determines whether the specified latitude and longitude coordinate points fall within the specified polygon area         ///</summary>        ///<param name= " ALon "> Point of Longitude </param>        ///<param name=" Alat "> Point of Latitude </ param>        ///<param name= "apoints" > Specify Polygon area node coordinates </param>        ///<returns>true fall within range False not in range </returns>          public bool Isptinpoly (double ALon, double Alat, point[] apoints)          {            int isum, icount, Iindex;             double DLon1, DLon2, DLAT1, DLAT2, Dlon;             if (apoints.length< 3)             {                 return false;            }              isum = 0;             icount = apoints.length;             for (iindex = 0; iindex < iCount-1 iindex++) &NB sp;           {                 if (iindex = iCount-1)                  {                     dLon1 = Apoints[iindex]. X                     DLAT1 = Apoints[iindex]. Y                      DLon2 = apoints[0]. X                      DLAT2 = apoints[0]. Y                }                  Else                  {                     dLon1 = Apoints[iindex]. X                      DLAT1 = Apoints[iindex]. Y                     DLon2 = Apoints[iindex + 1]. X                      DLAT2 = Apoints[iindex + 1]. Y                }                  if ((Alat >= dLat1) && (Alat < DLAT2)) | | ((Alat >= dLat2) && (Alat < DLAT1))                 {                     if (Math.Abs ( DLAT1-DLAT2) > 0)                      {