distanceVector static method
Get distance between v1
and v2
Implementation
static double distanceVector(Vec3 v1,Vec3 v2 ){
double xd = v1.x - v2.x;
double yd = v1.y - v2.y;
double zd = v1.z - v2.z;
return xd * xd + yd * yd + zd * zd;
}