点到直线的距离 点是否在多边形内 计算多边形面积 四边形面积 三角形面积 两边之和减去第三边 C程序

typedef struct CvPoint{

     int x,

     int y

}CvPoint;

 

//点是否在多边形里面
bool PtInPolygon(CvPoint p,CvPoint* ptpolygon,int nCount)
{
    int nCross=0;
    for (int i=0;i < nCount;i++)
   {
       CvPoint p1=ptpolygon[i];
       CvPoint p2=ptpolygon[(i + 1) % nCount];

       //求解 y=p.y 与 p1p2 的交点
       if (p1.y == p2.y) //p1p2与y=po.y平行
              continue;
      if (p.y < min(p1.y,p2.y))  //交点在p1p2延长线上
             continue;
       if (p.y >=max(p1.y,p2.y))//交点在p1p2延长线上
               continue;
      //求交点的x坐标
       double x=(double)(p.y - p1.y) * (double)(p2.x - p1.x) / (double)(p2.y - p1.y) + p1.x;
        if (x>p.x)
                   nCross++; //只统计单边交点
 }
 return (nCross % 2 == 1);
}

 

 

// 计算多边形面积

double PolygonArea(CvPoint* pVertex, int NUM){

 double fArea = 0;
 for(int i = 0; i < NUM - 1; i++){
  fArea += (0.5 * (pVertex[i].x * pVertex[i + 1].y - pVertex[i].y * pVertex[i + 1].x));}
 return fArea;
}
//计算四边形的面积
double SquArea(int x1,int y1,int x2, int y2, int x3,int y3,int x4,int y4)
{
 double T_area1,T_area2,S_area;
 T_area1=TrianglArea(  x1,y1,x2,y2, x3,y3);
 T_area2=TrianglArea( x1,y1,x4,y4, x3,y3);
 S_area=T_area1+T_area2;
 return S_area;
}
//计算三角型面积的函数
double TrianglArea( int x1,int y1,int x2, int y2, int x3,int y3)
{

 
 double a,b,c,s,T_area;
 
 a=sqrt((double)(pow((double)(x2-x1),2)+pow((double)(y2-y1),2)));
 b=sqrt((double)(pow((double)(x3-x2),2)+pow((double)(y3-y2),2)));
 c=sqrt((double)(pow((double)(x3-x1),2)+pow((double)(y3-y1),2)));
 if((a+b>c)&&(a+c>b)&&(b+c>a))
 {
  s=(a+b+c)/2;
  T_area=sqrt(s*(s-a)*(s-b)*(s-c));
 }
 else
  //不能构成三角形
  T_area=0.;
 return T_area;
}

//计算两边之和减去第三边
double Distance2(int x1,int y1,int x2, int y2, int x3,int y3)
{
 double T_distance,a,b,c;
 a=sqrt((double)(pow((double)(x2-x1),2)+pow((double)(y2-y1),2)));//质心到两点的距离 a，b
 b=sqrt((double)(pow((double)(x3-x1),2)+pow((double)(y3-y1),2)));
 c=sqrt((double)(pow((double)(x3-x2),2)+pow((double)(y3-y2),2)));
 T_distance=a+b-c;
 return T_distance;
}
bool Direcetion(CvPoint P1,CvPoint P2,CvPoint P3)
{
 int a = 0,b = 0,c = 0;
 int x1,y1;
 
 if(P2.y >= P3.y)
 {
  a = P2.y - P3.y;
  b = P3.x - P2.x;
  c = P3.y * P2.x - P3.x * P2.y;
 }
 else
 {
  a = P3.y - P2.y;
  b = P2.x - P3.x;
  c = P2.y * P3.x - P2.x * P3.y;
 }
 y1 = P1.y;
 x1 = (-b*y1-c) / a;
 if (P1.x<=x1)
 {
  return true;
 }
 else
  return false;
}

 

//点到直线的距离 直线由两点p2、p3决定  ax+by+c=0
//计算点P1到直线P2P3的距离

double Distance(CvPoint P1,CvPoint P2,CvPoint P3)
{
 double s = 0;
 double a = 0,b = 0,c = 0;

 if(P2.y >= P3.y)
 {
  a = P2.y - P3.y;
  b = P3.x - P2.x;
  c = P3.y * P2.x - P3.x * P2.y;
 }
 else
 {
  a = P3.y - P2.y;
  b = P2.x - P3.x;
  c = P2.y * P3.x - P2.x * P3.y;
 }
 
 s = fabs(a * P1.x + b * P1.y + c) / sqrt( a * a + b * b);

 return s;
}