How to use the discretize.utils.refine_tree_xyz function in discretize

# Define the base mesh
hx = [(dx, nbcx)]
hy = [(dy, nbcy)]
hz = [(dz, nbcz)]
mesh = TreeMesh([hx, hy, hz], x0='CCN')

# Refine based on surface topography
mesh = refine_tree_xyz(
    mesh, topo, octree_levels=[2, 2], method='surface', finalize=False
)

# Refine box base on region of interest
xp, yp, zp = np.meshgrid([-100., 100.], [-100., 100.], [-80., 0.])
xyz = np.c_[mkvc(xp), mkvc(yp), mkvc(zp)]

mesh = refine_tree_xyz(
    mesh, xyz, octree_levels=[2, 2], method='box', finalize=False
)

mesh.finalize()

##########################################################
# Create Magnetic Vector Intensity Model (MVI)
# --------------------------------------------
#
# Magnetic vector models are defined by three-component effective
# susceptibilities. To create a magnetic vector
# model, we must
#
#     1) Define the magnetic susceptibility for each cell. Then multiply by the
#     unit vector direction of the inducing field. (induced contribution)
#     2) Define the remanent magnetization vector for each cell and normalized

mesh = TreeMesh([hx, hy, hz], x0='CCN')

# Mesh refinement based on topography
mesh = refine_tree_xyz(
    mesh, topo_xyz, octree_levels=[0, 0, 0, 0, 1], method='surface', finalize=False
)

# Mesh refinement near transmitters and receivers
mesh = refine_tree_xyz(
    mesh, electrode_locs, octree_levels=[2, 4], method='radial', finalize=False
)

# Refine core mesh region
xp, yp, zp = np.meshgrid([-600., 600.], [-300., 300.], [-500., 0.])
xyz = np.c_[mkvc(xp), mkvc(yp), mkvc(zp)]
mesh = refine_tree_xyz(
    mesh, xyz, octree_levels=[0, 2, 2], method='box', finalize=False
    )

mesh.finalize()

###############################################################
# Create Conductivity Model and Mapping for OcTree Mesh
# -----------------------------------------------------
#
# Here we define the conductivity model that will be used to predict DC
# resistivity data. The model consists of a conductive sphere and a
# resistive sphere within a moderately conductive background. Note that
# you can carry through this work flow with a resistivity model if desired.
#

# Define conductivity model in S/m (or resistivity model in Ohm m)

# Create OcTree Mesh
# ------------------
#
# Here we define the OcTree mesh that is used for this example.
#

dh = 20.                                                     # base cell width
dom_width = 3000.                                            # domain width
nbc = 2**int(np.round(np.log(dom_width/dh)/np.log(2.)))      # num. base cells

# Define the base mesh
h = [(dh, nbc)]
mesh = TreeMesh([h, h, h], x0='CCC')

# Mesh refinement based on topography
mesh = refine_tree_xyz(
    mesh, topo_xyz, octree_levels=[0, 0, 0, 1], method='surface', finalize=False
)

# Mesh refinement near transmitters and receivers
mesh = refine_tree_xyz(
    mesh, rx_locs, octree_levels=[2, 4], method='radial', finalize=False
)

# Refine core mesh region
xp, yp, zp = np.meshgrid([-300., 300.], [-300., 300.], [-400., 0.])
xyz = np.c_[mkvc(xp), mkvc(yp), mkvc(zp)]
mesh = refine_tree_xyz(
    mesh, xyz, octree_levels=[0, 2, 4], method='box', finalize=False
)

mesh.finalize()

# Define the base mesh
hx = [(dx, nbcx)]
hy = [(dy, nbcy)]
hz = [(dz, nbcz)]
mesh = TreeMesh([hx, hy, hz], x0='CCN')

# Refine based on surface topography
mesh = refine_tree_xyz(
    mesh, topo, octree_levels=[2, 2], method='surface', finalize=False
)

# Refine box based on region of interest
xp, yp, zp = np.meshgrid([-100., 100.], [-100., 100.], [-80., 0.])
xyz = np.c_[mkvc(xp), mkvc(yp), mkvc(zp)]

mesh = refine_tree_xyz(
    mesh, xyz, octree_levels=[2, 2], method='box', finalize=False
)

mesh.finalize()

#######################################################
# Density Contrast Model and Mapping on OcTree Mesh
# -------------------------------------------------
#
# Here, we create the density contrast model that will be used to predict gravity gradiometry
# data and the mapping from the model to the mesh. The model
# consists of a less dense block and a more dense sphere.
#

# Define density contrast values for each unit in g/cc
background_val = 0.

# resistivity and IP data.
#

dh = 10.                                                    # base cell width
dom_width_x = 2400.                                         # domain width x                                        # domain width y
dom_width_z = 1200.                                         # domain width z
nbcx = 2**int(np.round(np.log(dom_width_x/dh)/np.log(2.)))  # num. base cells x
nbcz = 2**int(np.round(np.log(dom_width_z/dh)/np.log(2.)))  # num. base cells z

# Define the base mesh
hx = [(dh, nbcx)]
hz = [(dh, nbcz)]
mesh = TreeMesh([hx, hz], x0='CN')

# Mesh refinement based on topography
mesh = refine_tree_xyz(
    mesh, topo_xyz[:, [0, 2]], octree_levels=[1], method='surface', finalize=False
)

# Mesh refinement near transmitters and receivers
dc_survey.getABMN_locations()
electrode_locations = np.r_[
    dc_survey.a_locations, dc_survey.b_locations,
    dc_survey.m_locations, dc_survey.n_locations
    ]

unique_locations = np.unique(electrode_locations, axis=0)

mesh = refine_tree_xyz(
    mesh, unique_locations, octree_levels=[2, 4], method='radial', finalize=False
)

# resistivity and IP data.
#

dh = 10.                                                    # base cell width
dom_width_x = 2400.                                         # domain width x
dom_width_z = 1200.                                         # domain width z
nbcx = 2**int(np.round(np.log(dom_width_x/dh)/np.log(2.)))  # num. base cells x
nbcz = 2**int(np.round(np.log(dom_width_z/dh)/np.log(2.)))  # num. base cells z

# Define the base mesh
hx = [(dh, nbcx)]
hz = [(dh, nbcz)]
mesh = TreeMesh([hx, hz], x0='CN')

# Mesh refinement based on topography
mesh = refine_tree_xyz(
    mesh, xyz_topo[:,[0, 2]], octree_levels=[1], method='surface', finalize=False
)

# Mesh refinement near transmitters and receivers. First we need to obtain the
# set of unique electrode locations.
dc_survey.getABMN_locations()
electrode_locations = np.c_[
    dc_survey.a_locations, dc_survey.b_locations,
    dc_survey.m_locations, dc_survey.n_locations
    ]

unique_locations = np.unique(
    np.reshape(electrode_locations, (4*dc_survey.nD, 2)), axis=0
    )

mesh = refine_tree_xyz(

dh = 25.                                                     # base cell width
dom_width = 1600.                                            # domain width
nbc = 2**int(np.round(np.log(dom_width/dh)/np.log(2.)))      # num. base cells

# Define the base mesh
h = [(dh, nbc)]
mesh = TreeMesh([h, h, h], x0='CCC')

# Mesh refinement based on topography
mesh = refine_tree_xyz(
    mesh, topo_xyz, octree_levels=[0, 0, 0, 1], method='surface', finalize=False
)

# Mesh refinement near transmitters and receivers
mesh = refine_tree_xyz(
    mesh, rx_locs, octree_levels=[2, 4], method='radial', finalize=False
)

# Refine core mesh region
xp, yp, zp = np.meshgrid([-300., 300.], [-300., 300.], [-300., 0.])
xyz = np.c_[mkvc(xp), mkvc(yp), mkvc(zp)]
mesh = refine_tree_xyz(
    mesh, xyz, octree_levels=[0, 2, 4], method='box', finalize=False
)

mesh.finalize()

###############################################################
# Create Resistivity Model and Mapping for OcTree Mesh
# ----------------------------------------------------
#

# Create OcTree Mesh
# ------------------
#
# Here we define the OcTree mesh that is used for this example.
#

dh = 25.                                                     # base cell width
dom_width = 1600.                                            # domain width
nbc = 2**int(np.round(np.log(dom_width/dh)/np.log(2.)))      # num. base cells

# Define the base mesh
h = [(dh, nbc)]
mesh = TreeMesh([h, h, h], x0='CCC')

# Mesh refinement based on topography
mesh = refine_tree_xyz(
    mesh, topo_xyz, octree_levels=[0, 0, 0, 1], method='surface', finalize=False
)

# Mesh refinement near transmitters and receivers
mesh = refine_tree_xyz(
    mesh, rx_locs, octree_levels=[2, 4], method='radial', finalize=False
)

# Refine core mesh region
xp, yp, zp = np.meshgrid([-300., 300.], [-300., 300.], [-300., 0.])
xyz = np.c_[mkvc(xp), mkvc(yp), mkvc(zp)]
mesh = refine_tree_xyz(
    mesh, xyz, octree_levels=[0, 2, 4], method='box', finalize=False
)

mesh.finalize()

mesh = TreeMesh([h, h, h], x0='CCC')

# Mesh refinement based on topography
mesh = refine_tree_xyz(
    mesh, topo_xyz, octree_levels=[0, 0, 0, 1], method='surface', finalize=False
)

# Mesh refinement near transmitters and receivers
mesh = refine_tree_xyz(
    mesh, rx_locs, octree_levels=[2, 4], method='radial', finalize=False
)

# Refine core mesh region
xp, yp, zp = np.meshgrid([-300., 300.], [-300., 300.], [-300., 0.])
xyz = np.c_[mkvc(xp), mkvc(yp), mkvc(zp)]
mesh = refine_tree_xyz(
    mesh, xyz, octree_levels=[0, 2, 4], method='box', finalize=False
)

mesh.finalize()

###############################################################
# Create Resistivity Model and Mapping for OcTree Mesh
# ----------------------------------------------------
#
# Here, we define the electrical properties of the Earth as a resistivity
# model. The model consists of a long vertical conductive pipe within a more
# resistive background.
#

# Log-Resistivity in log[Ohm m]
air_val = 1e8

# Mesh refinement based on topography
mesh = refine_tree_xyz(
    mesh, topo_xyz[:, [0, 2]], octree_levels=[1], method='surface', finalize=False
)

# Mesh refinement near transmitters and receivers
dc_survey.getABMN_locations()
electrode_locations = np.r_[
    dc_survey.a_locations, dc_survey.b_locations,
    dc_survey.m_locations, dc_survey.n_locations
    ]

unique_locations = np.unique(electrode_locations, axis=0)

mesh = refine_tree_xyz(
    mesh, unique_locations, octree_levels=[2, 4], method='radial', finalize=False
)

# Refine core mesh region
xp, zp = np.meshgrid([-800., 800.], [-800., 0.])
xyz = np.c_[mkvc(xp), mkvc(zp)]
mesh = refine_tree_xyz(
    mesh, xyz, octree_levels=[0, 2, 2], method='box', finalize=False
    )

mesh.finalize()


###############################################################
# Project Surveys to Discretized Topography
# -----------------------------------------