已知3点,求平面方程,点到面的距离

//已知3点，求平面方程
BOOL CGe::PanelEquationFromThreePt(CPoint3dArray ptArr,
double &a,double &b,double &c,double &d)
{//from http://blog.csdn.net/hoya5121 CPoint3d p1,p2,p3;

if(ptArr.GetSize() < 3)
{
return FALSE;
}
p1 = ptArr[0];
p2 = ptArr[1];
p3 = ptArr[2];

a = ( (p2.y-p1.y)*(p3.z-p1.z)-(p2.z-p1.z)*(p3.y-p1.y) );
b = ( (p2.z-p1.z)*(p3.x-p1.x)-(p2.x-p1.x)*(p3.z-p1.z) );
c = ( (p2.x-p1.x)*(p3.y-p1.y)-(p2.y-p1.y)*(p3.x-p1.x) );
d = ( 0-(a*p1.x+b*p1.y+c*p1.z) );

return TRUE;
}

//点到面的距离，设点坐标为P(x, y, z)，平面方程为ax+by+cz+d=0。
double CGe::DistPt2Panel( double x,double y,double z,
double a,double b,double c,double d)
{
return fabs(a*x+b*y+c*z+d) / sqrt(a*a+b*b+c*c);
}