double CMap3DEditorDoc::det(gpc_vertex p0, gpc_vertex p1, gpc_vertex p2)
{  return (p1.x-p0.x)*(p2.y-p0.y)-(p1.y-p0.y)*(p2.x-p0.x);
}  double CMap3DEditorDoc::ploygon_area(int n,gpc_vertex p[])
{  double s=0.0f;  int i=1;  for(;i < n-1;i++)  s += det(p[0],p[i],p[i+1]);  return 0.5*fabs(s);
} 

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typedef struct                      /* Polygon vertex structure          */
{double              x;            /* Vertex x component                */double              y;            /* vertex y component                */
} gpc_vertex;

typedef struct                      /* Polygon set structure             */
{int                 num_contours; /* Number of contours in polygon     */int                *hole;         /* Hole / external contour flags     */gpc_vertex_list    *contour;      /* Contour array pointer             */
} gpc_polygon;

typedef struct                      /* Vertex list structure             */
{int                 num_vertices; /* Number of vertices in list        */gpc_vertex         *vertex;       /* Vertex array pointer              */
} gpc_vertex_list;

double CMap3DEditorDoc::CalIntersectRegion(CSMAPFace *pSubject_Face, CSMAPFace *pClip_Face)
{if(!pSubject_Face || !pClip_Face) return 0;gpc_polygon *psubject_polygon = new gpc_polygon;//第一个多边形数据gpc_polygon *pclip_polygon = new gpc_polygon;//第二个多边形数据gpc_polygon *presult_polygon = new gpc_polygon; //交集多边形数据psubject_polygon->num_contours = pclip_polygon->num_contours = presult_polygon->num_contours = 1;psubject_polygon->hole = pclip_polygon->hole = presult_polygon->hole = 0;//初始化FaceToPolygon(pSubject_Face, psubject_polygon);//转化第一个多边形数据成gpc_polygonFaceToPolygon(pClip_Face, pclip_polygon);//转化第二个数据gpc_polygon_clip(GPC_INT, psubject_polygon, pclip_polygon, presult_polygon);//运用交差并补函数,GPC_INT指进行交运算if(!presult_polygon->num_contours) return 0;double area = ploygon_area(presult_polygon->contour->num_vertices, presult_polygon->contour->vertex);psubject_polygon=pclip_polygon=presult_polygon=NULL;delete presult_polygon;delete pclip_polygon;delete presult_polygon;return area;}