已知三维空间内三点坐标，求三角形面积（简单）

//求三角形面积;
//返回-1为不能组成三角形;
double count_triangle_area(Point a,Point b,Point c){
double area = -1;

double side[3];//存储三条边的长度;

side[0] = sqrt(pow(a.x - b.x,2)+pow(a.y - b.y,2) + pow(a.z - b.z,2)); 
side[1] = sqrt(pow(a.x - c.x,2)+pow(a.y - c.y,2) + pow(a.z - c.z,2));
side[2] = sqrt(pow(c.x - b.x,2)+pow(c.y - b.y,2) + pow(c.z - b.z,2)); 

//不能构成三角形;
if(side[0]+side[1]<=side[2] || side[0]+side[2]<=side[1] || side[1]+side[2]<=side[0]) return area; 

//利用海伦公式。s=sqr(p*(p-a)(p-b)(p-c)); 
double p = (side[0]+side[1]+side[2])/2; //半周长;
area = sqrt(p*(p-side[0])*(p-side[1])*(p-side[2])); 

return area;
}