tl;dr: vtkDataSetTriangleFilter causes cell connectivity ordering to change for pure vtk unstructured grid but not in a pyvista uns grid. Why? Does it matter? What am I missing to replicate the latter effect given that pyvista wraps vtk?
I have a pyvista fn that creates a tetrahedron unstructured grid and I translated it to pure vtk as such:
from vtkmodules.vtkCommonDataModel import (
VTK_HEXAHEDRON,
VTK_TETRA,
VTK_TRIANGLE,
vtkDataSet,
vtkPolyData,
vtkUnstructuredGrid,
)
from vtkmodules.util import numpy_support
import numpy as np
import pyvista as pv
from vtkmodules.vtkCommonCore import vtkIdList, vtkPoints, vtkStringArray
from vtkmodules.vtkFiltersGeneral import vtkDataSetTriangleFilter
# pyvista:
def get_tetra(cell_num: int = 2):
points_per_cell = 4
points = np.empty((points_per_cell * cell_num, 3), dtype=np.float32)
for i in range(cell_num):
points[i*points_per_cell : (i+1)*points_per_cell] = \
[[i, 0, 0],[i+0.5, 0, 0],[i+0.5, 0.5, 0.5],[i, 0, 0.5]] # fmt: skip
cells = np.arange(len(points)).reshape([cell_num, points_per_cell])
grid = pv.UnstructuredGrid({VTK_TETRA: cells}, points)
return grid
pv_tetra = get_tetra()
# pure vtk:
def get_unstructured_grid(cell_num: int = 2):
grid = vtkUnstructuredGrid()
points = vtkPoints()
point_idx = 0
def insert_cell(cell_type_id, point_ids):
id_list = vtkIdList()
for pid in point_ids:
id_list.InsertNextId(pid)
grid.InsertNextCell(cell_type_id, id_list)
for i in range(cell_num):
cell_points = np.array(
[
[i, 0, 0],
[i + 0.5, 0, 0],
[i + 0.5, 0.5, 0.5],
[i, 0, 0.5],
],
dtype=np.float32,
)
ids = []
for pt in cell_points:
points.InsertNextPoint(pt)
ids.append(point_idx)
point_idx += 1
id_list = vtkIdList()
for pid in ids:
id_list.InsertNextId(pid)
grid.InsertNextCell(VTK_TETRA, id_list)
grid.SetPoints(points)
return grid
vtk_ugrid = get_unstructured_grid()
These two seem identical:
However, using the vtkDataSetTriangleFilter on them yields different results in connectivity ordering:
print(numpy_support.vtk_to_numpy(pv_tetra.GetCells().GetData()))
print(numpy_support.vtk_to_numpy(vtk_ugrid.GetCells().GetData()))
trifilter = vtkDataSetTriangleFilter(input_data=pv_tetra)
trifilter.Update()
new_pv_tetra = trifilter.GetOutput()
trifilter1 = vtkDataSetTriangleFilter(input_data=vtk_ugrid)
trifilter1.Update()
new_vtk_ugrid = trifilter1.GetOutput()
print(numpy_support.vtk_to_numpy(new_pv_tetra.GetCells().GetData()))
print(numpy_support.vtk_to_numpy(new_vtk_ugrid.GetCells().GetData()))
yields
[4 0 1 2 3 4 4 5 6 7]
[4 0 1 2 3 4 4 5 6 7]
[4 0 1 2 3 4 4 5 6 7]
[4 1 2 0 3 4 5 6 4 7]
Why does the connectivity ordering change in the pure vtk implementation but not the pyvista implementation? What can I do to replicate the latter? What are the implications of the connectivity ordering changing?
Thanks!