Bug: Accessing TreeMesh.cell_centers before finalization produces invalid mesh

[santisoler]

When creating a TreeMesh, if we access the cell_centers attribute before we finalize the mesh we end up getting an invalid mesh with an empty array for the cell_centers after we do finalize it.

The following example works as expected and a valid mesh is created:

import numpy as np
import discretize

# Minimum cell widths
dx, dy = 5, 5

# Mesh lengths along each direction
x_length, y_length = 300.0, 300.0

# Compute number of base mesh cells required in x and y
nbcx = 2 ** int(np.round(np.log2(x_length / dx)))
nbcy = 2 ** int(np.round(np.log2(y_length / dy)))

# Define the base mesh
hx = [(dx, nbcx)]
hy = [(dy, nbcy)]
mesh = discretize.TreeMesh([hx, hy], x0="CC")

# Refine near points
xx = np.array([0.0, 10.0, 0.0, -10.0])
yy = np.array([-20.0, -10.0, 0.0, -10])
pts = np.c_[discretize.utils.mkvc(xx), discretize.utils.mkvc(yy)]
mesh = discretize.utils.refine_tree_xyz(
    mesh, pts, octree_levels=[2, 2], method="radial", finalize=False
)

mesh.finalize()

print(mesh)
print("\nSize of cell_centers:", mesh.cell_centers.size)

QuadTreeMesh: 4.64% filled

Level : Number of cells               Mesh Extent               Cell Widths    
-----------------------           min     ,     max            min   ,   max   
  2   :        4             ---------------------------   --------------------
  3   :       34          x:    -160.0    ,    160.0          5.0    ,    80.0   
  4   :       36          y:    -160.0    ,    160.0          5.0    ,    80.0   
  5   :       68       
  6   :       48       
-----------------------
Total :       190      

Size of cell_centers: 380

But if we access mesh.cell_centers before running mesh.finalize(), the mesh.cell_centers array is empty, making impossible to use this mesh in any further step (inversion, plotting, etc).

import numpy as np
import discretize

# Minimum cell widths
dx, dy = 5, 5

# Mesh lengths along each direction
x_length, y_length = 300.0, 300.0

# Compute number of base mesh cells required in x and y
nbcx = 2 ** int(np.round(np.log2(x_length / dx)))
nbcy = 2 ** int(np.round(np.log2(y_length / dy)))

# Define the base mesh
hx = [(dx, nbcx)]
hy = [(dy, nbcy)]
mesh = discretize.TreeMesh([hx, hy], x0="CC")

# Refine near points
xx = np.array([0.0, 10.0, 0.0, -10.0])
yy = np.array([-20.0, -10.0, 0.0, -10])
pts = np.c_[discretize.utils.mkvc(xx), discretize.utils.mkvc(yy)]
mesh = discretize.utils.refine_tree_xyz(
    mesh, pts, octree_levels=[2, 2], method="radial", finalize=False
)

print(mesh.cell_centers)
mesh.finalize()

print(mesh)
print("\nSize of cell_centers:", mesh.cell_centers.size)

[]

QuadTreeMesh: 4.64% filled

Level : Number of cells               Mesh Extent               Cell Widths    
-----------------------           min     ,     max            min   ,   max   
  2   :        4             ---------------------------   --------------------
  3   :       34          x:    -160.0    ,    160.0          5.0    ,    80.0   
  4   :       36          y:    -160.0    ,    160.0          5.0    ,    80.0   
  5   :       68       
  6   :       48       
-----------------------
Total :       190      

Size of cell_centers: 0

cc @lheagy

[jcapriot]

We need to add guards for a lot of the attributes of the TreeMesh so they cannot be accessed until the mesh is finalized.