三维空间已知两个点坐标及在该直线上未知点到其中一个点的距离，求该未知点的坐标

class CPoint
{
public:
 CPoint()
  {
   x = 0.0f;
   y = 0.0f;
   z = 0.0f;
 }

 double x;
 double y;
 double z;
};

CPoint CPointInfo::getPoint( CPoint p1, CPoint p2, double mDistance )
{
  CPoint point;
 double distance = getDistance(p1,p2);
 double theta = asin((p2.z-p1.z)/distance);

  point.x = p1.x+mDistance/cos(theta)/distance*(p2.x-p1.x);
 point.y = p1.y+mDistance/cos(theta)/distance*(p2.y-p1.y);
 point.z = p1.z+mDistance/cos(theta)/distance*(p2.z-p1.z);
 return point;
}

double CPointInfo::getDistance( CPoint p1, CPoint p2 )
{
 return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)+(p1.z-p2.z)*(p1.z-p2.z));
}