// Given point P, find the point on the line defined by A and B that is closest to point B
vector getClosetPoint(vector A, vector B, vector P)
{
    vector AP = P - A;
    vector AB = B - A;
    return A + AB * ((AP.x*AB.x + AP.y*AB.y + AP.z*AB.z) / (AB.x*AB.x + AB.y*AB.y + AB.z*AB.z));
}