  Magnetic fields are a defining yet enigmatic aspect of the interstellar
medium (ISM), with their three-dimensional mapping posing a substantial
challenge. In this study, we harness the innovative Velocity Gradient Technique
(VGT), underpinned by magnetohydrodynamic (MHD) turbulence theories, to
elucidate the magnetic field structure by applying it to the atomic neutral
hydrogen (HI) emission line and the molecular tracer $^{12}$CO. We construct
the tomography of the magnetic field in the low-mass star-forming region L1688,
utilizing two approaches: (1) VGT-HI combined with the Galactic rotational
curve, and (2) stellar polarization paired with precise star parallax
measurements. Our analysis reveals that the magnetic field orientations deduced
from stellar polarization undergo a distinct directional change in the vicinity
of L1688, providing evidence that the misalignment between VGT-HI and stellar
polarization stems from the influence of the molecular cloud's magnetic field
on the polarization of starlight. When comparing VGT-$^{12}$CO to stellar
polarization and Planck polarization data, we observe that VGT-$^{12}$CO
effectively reconciles the misalignment noted with VGT-HI, showing statistical
alignment with Planck polarization measurements. This indicates that
VGT-$^{12}$CO could be integrated with VGT-HI, offering vital insights into the
magnetic fields of molecular clouds, thereby enhancing the accuracy of our 3D
magnetic field reconstructions.
