Re: More on VTK objects and mesh plotting with 3rd party packaages

[Guyer, Jonathan E. Dr. (Fed) via fipy]

> On Feb 23, 2020, at 8:43 AM, A A <amine.aboufir...@gmail.com> wrote:
> 
> Uncommenting line 7 of the above code reveals that resetting the cell type 
> from 41 to 7 of the UniformGrid2D's underlying tvtk object allows the mesh to 
> appear in the plotter. 
> 
> I recall from previous discussions that failure of cell type 41 to plot was 
> attributed to incorrect ordering of the cell vertices, but this would be in 
> contradiction with the results of the code above.


>From the [VTK 
>documentation](https://vtk.org/doc/release/4.2/html/classvtkConvexPointSet.html),
> "vtkConvexPointSet is a concrete implementation that represents a 3D cell 
>defined by a convex set of points." FiPy does not output vertices correctly 
>for this 3D object. The fact that a Grid2D outputs its vertices in the correct 
>order for a VTK_POLYGON does not change the fact that the ordering is wrong 
>for VTK_CONVEX_POINT_SET.

The docstring for UniformGrid2D._calcOrderedCellVertexIDs says "Correct 
ordering for VTK_PIXEL", but it does not do this. It produces the ordering for 
VTK_QUAD (which also works for VTK_POLYGON).

The docstring for UniformGrid3D._calcOrderedCellVertexIDs correctly states 
"Correct ordering for `VTK_VOXEL`".

The proper interim fix is to make the following changes:

diff --git a/fipy/meshes/nonUniformGrid3D.py b/fipy/meshes/nonUniformGrid3D.py
index 8e78c5319..03097e2b7 100644
--- a/fipy/meshes/nonUniformGrid3D.py
+++ b/fipy/meshes/nonUniformGrid3D.py
@@ -116,6 +116,14 @@ class NonUniformGrid3D(Mesh):
         faceTangents2[2, self.numberOfXYFaces + self.numberOfXZFaces:] = 1.
         return faceTangents1, faceTangents2
 
+    @property
+    def _VTKCellType(self):
+        try:
+            from tvtk.api import tvtk
+        except ImportError as e:
+            from enthought.tvtk.api import tvtk
+        return tvtk.Voxel().cell_type
+
 ## The following method is broken when dx, dy or dz are not scalar. Simpler to 
use the generic
 ## _calcFaceAreas rather than do the required type checking, resizing and 
outer product.
 ##
diff --git a/fipy/meshes/uniformGrid1D.py b/fipy/meshes/uniformGrid1D.py
index 041f8ed9d..931f3f708 100644
--- a/fipy/meshes/uniformGrid1D.py
+++ b/fipy/meshes/uniformGrid1D.py
@@ -288,6 +288,14 @@ class UniformGrid1D(UniformGrid):
         c1 = numerix.arange(self.numberOfCells)
         return numerix.array((c1 + 1, c1))
 
+    @property
+    def _VTKCellType(self):
+        try:
+            from tvtk.api import tvtk
+        except ImportError as e:
+            from enthought.tvtk.api import tvtk
+        return tvtk.Line().cell_type
+
     def _getNearestCellID(self, points):
         """
         Test cases
diff --git a/fipy/meshes/uniformGrid2D.py b/fipy/meshes/uniformGrid2D.py
index 16815c689..37d3ebfa6 100644
--- a/fipy/meshes/uniformGrid2D.py
+++ b/fipy/meshes/uniformGrid2D.py
@@ -560,6 +560,14 @@ class UniformGrid2D(UniformGrid):
 
         return ids.reshape((4, self.numberOfCells), order='F')
 
+    @property
+    def _VTKCellType(self):
+        try:
+            from tvtk.api import tvtk
+        except ImportError as e:
+            from enthought.tvtk.api import tvtk
+        return tvtk.Quad().cell_type
+
     def _getNearestCellID(self, points):
         """
         Test cases
diff --git a/fipy/meshes/uniformGrid3D.py b/fipy/meshes/uniformGrid3D.py
index 4ad7a3b69..29990f53e 100644
--- a/fipy/meshes/uniformGrid3D.py
+++ b/fipy/meshes/uniformGrid3D.py
@@ -491,6 +491,14 @@ class UniformGrid3D(UniformGrid):
 
         return numerix.reshape(ids.swapaxes(1, 3), (8, self.numberOfCells))
 
+    @property
+    def _VTKCellType(self):
+        try:
+            from tvtk.api import tvtk
+        except ImportError as e:
+            from enthought.tvtk.api import tvtk
+        return tvtk.Voxel().cell_type
+
 ##     scaling
 
     def _getNearestCellID(self, points):


This will fix the Grid classes. It definitely doesn't fix arbitrary 3D meshes.
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