Illustration of how VGT works. The MHD turbulent eddies (blue) are elongated along the local magnetic field (black line) directions. The gradients (red) of physical information of these eddies (e.g., densities without shock influences, velocities, or magnetic intensities) will therefore be maximally perpendicular to the local magnetic field directions. As a result, a simple 90^o rotation of gradients traces the direction of magnetic field locally.