Hi everyone,
I want to compute the normal vector field to a given 2D meshed surface (surf) embedded within R^3.
To that end, I use the ufl.CellNormal(surf) class (thk @dokken btw…).
Prior to any computation, I want to visualize this vector field. To that end, I wrote this code:
import pyvista as pv
import ufl
from dolfinx import fem, plot
vDG0 = fem.VectorFunctionSpace(surf, ('DG', 0))
# Compute the normal vector field
cell_nrl = ufl.CellNormal(surf)
nrl_expr = fem.Expression(cell_nrl, vDG0.element.interpolation_points())
normals = fem.Function(vDG0)
normals.interpolate(nrl_expr)
# Reshape the array
gdim = surf.geometry.dim
nbr_cell = sphere.topology.original_cell_index.shape[0]
nrl_vcts = normals.x.array.real.reshape((nbr_cell, gdim))
# Plot
topology, cell_types, geometry = plot.create_vtk_mesh(surf)
grid = pv.UnstructuredGrid(topology, cell_types, geometry)
grid['normals'] = nrl_vcts
glyphs = grid.glyph(orient='normals', factor=.1)
pltr = pv.Plotter()
pltr.add_mesh(grid, style='wireframe', color='k')
pltr.add_mesh(glyphs)
pltr.show()
This code produces the expected vector field but with no coherent orientation, see caption below.
From my experience doing similar things with “legacy” FEniCS, I remember harmonizing cell orientation thoughout the mesh prior to the computation of normals; with the method mesh.init_cell_orientation() if I recall properly… I looked for such a method in FEniCSx but was not able to find any…
My question: How can I produce a coherent cell orientation on a meshed surface in FEniCSx ?
Thx for your help guys.
cheers