added bbox class method to regular mesh

openmc/mesh.py

@@ -279,6 +279,7 @@ class StructuredMesh(MeshBase):
 
         return vtk_grid
 
+
 class RegularMesh(StructuredMesh):
     """A regular Cartesian mesh in one, two, or three dimensions
 
@@ -509,6 +510,49 @@ class RegularMesh(StructuredMesh):
 
         return mesh
 
+    @classmethod
+    def from_bounding_box(
+        cls,
+        bounding_box,
+        dimension=[100, 100, 100],
+        mesh_id=None,
+        name=''
+    ):
+        """Create mesh from an existing openmc cell, region, universe or
+        geometry by making use of the objects bounding box property.
+
+        Parameters
+        ----------
+        bounding_box : {openmc.Cell, openmc.Region, openmc.Universe, openmc.Geometry}
+            The object passed in will be used as a template for this mesh. The
+            bounding_box of the property of the object passed will be used to
+            set the lower_left and upper_right of the mesh instance
+        dimension : Iterable of int
+            The number of mesh cells in each direction.
+        mesh_id : int
+            Unique identifier for the mesh
+        name : str
+            Name of the mesh
+
+        Returns
+        -------
+        openmc.RegularMesh
+            RegularMesh instance
+
+        """
+        cv.check_type(
+            "bounding_box",
+            bounding_box,
+            (openmc.Cell, openmc.Region, openmc.Universe, openmc.Geometry),
+        )
+
+        mesh = cls(mesh_id, name)
+        mesh.lower_left = bounding_box.bounding_box[0]
+        mesh.upper_right = bounding_box.bounding_box[1]
+        mesh.dimension = dimension
+
+        return mesh
+
     def to_xml_element(self):
         """Return XML representation of the mesh
 

tests/unit_tests/test_mesh_from_bounding_box.py

@@ -0,0 +1,63 @@
+import numpy as np
+import openmc
+import pytest
+
+
+def test_mesh_from_cell():
+    """Tests a RegularMesh can be made from a Cell and the specified dimensions
+    are propagated through. Cell is not centralized"""
+    surface = openmc.Sphere(r=10, x0=2, y0=3, z0=5)
+    cell = openmc.Cell(region=-surface)
+
+    mesh = openmc.RegularMesh.from_bounding_box(cell, dimension=[7, 11, 13])
+    assert isinstance(mesh, openmc.RegularMesh)
+    assert np.array_equal(mesh.dimension, (7, 11, 13))
+    assert np.array_equal(mesh.lower_left, cell.bounding_box[0])
+    assert np.array_equal(mesh.upper_right, cell.bounding_box[1])
+
+
+def test_mesh_from_region():
+    """Tests a RegularMesh can be made from a Region and the default dimensions
+    are propagated through. Region is not centralized"""
+    surface = openmc.Sphere(r=1, x0=-5, y0=-3, z0=-2)
+    region = -surface
+
+    mesh = openmc.RegularMesh.from_bounding_box(region)
+    assert isinstance(mesh, openmc.RegularMesh)
+    assert np.array_equal(mesh.dimension, (100, 100, 100))  # default values
+    assert np.array_equal(mesh.lower_left, region.bounding_box[0])
+    assert np.array_equal(mesh.upper_right, region.bounding_box[1])
+
+
+def test_mesh_from_universe():
+    """Tests a RegularMesh can be made from a Universe and the default dimensions
+    are propagated through. Universe is centralized"""
+    surface = openmc.Sphere(r=42)
+    cell = openmc.Cell(region=-surface)
+    universe = openmc.Universe(cells=[cell])
+
+    mesh = openmc.RegularMesh.from_bounding_box(universe)
+    assert isinstance(mesh, openmc.RegularMesh)
+    assert np.array_equal(mesh.dimension, (100, 100, 100))  # default values
+    assert np.array_equal(mesh.lower_left, universe.bounding_box[0])
+    assert np.array_equal(mesh.upper_right, universe.bounding_box[1])
+
+
+def test_mesh_from_geometry():
+    """Tests a RegularMesh can be made from a Geometry and the default dimensions
+    are propagated through. Geometry is centralized"""
+    surface = openmc.Sphere(r=42)
+    cell = openmc.Cell(region=-surface)
+    universe = openmc.Universe(cells=[cell])
+    geometry = openmc.Geometry(universe)
+
+    mesh = openmc.RegularMesh.from_bounding_box(geometry)
+    assert isinstance(mesh, openmc.RegularMesh)
+    assert np.array_equal(mesh.dimension, (100, 100, 100))  # default values
+    assert np.array_equal(mesh.lower_left, geometry.bounding_box[0])
+    assert np.array_equal(mesh.upper_right, geometry.bounding_box[1])
+
+
+def test_error_from_unsupported_object():
+    with pytest.raises(TypeError):
+        openmc.RegularMesh.from_bounding_box("vacuum energy")