# How to define a vtkExplicitStructuredGrid?
**URL:** https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189
**Category:** ParaView Support
**Created:** [December 16, 2019, 1:55pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189 "2019-12-16T13:55:19Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 16, 2019, 1:55pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/1 "2019-12-16T13:55:19Z")
I am trying to get a grasp for how to define and append point and cell data to a vtkExplicitStructuredGrid structure ([https://blog.kitware.com/introducing-explicit-structured-grids-in-vtk-and-paraview](https://blog.kitware.com/introducing-explicit-structured-grids-in-vtk-and-paraview)), for use with ParaView through plugins by Python scripting.
I understand how to define and append point and cell data to a vtkStructuredGrid with the use of flat indexing.
I get a bit confused when looking at the “Detailed Description” section in the class reference [https://vtk.org/doc/nightly/html/classvtkExplicitStructuredGrid.html](https://vtk.org/doc/nightly/html/classvtkExplicitStructuredGrid.html), where it states that “The order and number of points is arbitrary”. As I understand the each cell in the grid should be a hexahedron and contribute with eight points to the grid?
I would be very grateful if someone could explain the basics of building this structure and associate attributes!
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 16, 2019, 2:12pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/2 "2019-12-16T14:12:36Z")
I will suggest reading the VTK user guide, chapter 16.2, about implicit geometries.
[https://www.kitware.com/products/books/VTKUsersGuide.pdf](https://www.kitware.com/products/books/VTKUsersGuide.pdf)
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 17, 2019, 9:58am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/3 "2019-12-17T09:58:30Z")
Thanks for your reply [mwestphal](https://discourse.paraview.org/u/mwestphal).
Is the generell principle then to set the dimensions (defining (i, j, k) space) of the structure, so that one can continue to insert one cell at a time following the order defined through " **for** k … ( **for** j … ( **for** i …))?
In contrast to setting a vtkStructuredGrid where the points defining the mesh can be set through a vtkPoints object.
If so, I’m failing to identify the methods that vtkExplicitStructuredGrid can access to realise such assignments.
Would it be possible to show a minimal example, e.g. a cube/cuboid consisting of 2x2x2 cells?
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 17, 2019, 10:01am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/4 "2019-12-17T10:01:52Z")
Tools -\> Manage Plugins -\> Explicit Structured Grid -\> Load
Source -\> ExplicitStructuredGridGenerator.
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 17, 2019, 10:41am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/5 "2019-12-17T10:41:34Z")
Yes, I already looked at python-scripts generated after adding an ExplicitStructuredGridGenerator to the pipeline, but failed to see how to actually define a structure explicitly from own data, defined in a script or read from file into a generating script.
Maybe I was a bit unclear in my question? 🙂
The goal here is a Python-scripted ParaView-plugin that reads structure-data and attribute-data from file and generates an Explicit Structured Grid with cell data.
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 17, 2019, 11:08am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/6 "2019-12-17T11:08:05Z")
See here :
[https://gitlab.kitware.com/paraview/paraview/blob/master/Plugins/ExplicitStructuredGrid/Filter/vtkExplicitStructuredGridGeneratorSource.cxx](https://gitlab.kitware.com/paraview/paraview/blob/master/Plugins/ExplicitStructuredGrid/Filter/vtkExplicitStructuredGridGeneratorSource.cxx)
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 17, 2019, 1:21pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/7 "2019-12-17T13:21:33Z")
Thanks!
This surely points (🙂) in the right direction.
I’m trying to replicate the structure used in one of the methods in the C++ source file, using Python. Now stuck at assigning points inside the i-j-k loop, i.e., assignments like this one
`indice[0] = points->InsertNextPoint(i - 0.5, j - 0.5, GetZShift1(k - 0.5));`
How can the points be set with Python?
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 17, 2019, 1:58pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/8 "2019-12-17T13:58:41Z")
See here for examples of creating points in python :
[https://www.paraview.org/Wiki/Python\_Programmable\_Filter](https://www.paraview.org/Wiki/Python_Programmable_Filter)
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 18, 2019, 10:49am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/9 "2019-12-18T10:49:36Z")
Is it the Helix example you are referring to?
In that case I fail to find the equivalent methods for fixing/adding the cells.
The code that I manage to run so far is listed below. The cells are not working properly, changing Outline to Surface or Surface with Edges. Adding spherical glypsh gives the following output
I’m expecting one sphere in each corner, but there’s only two of those corners.
Each edge should have two spheres and each face should have have four spheres.
Is there a reason some points are missing? Is it related to the missing cell structure?
How can one fix the code so the cells gets properly defined?
```auto
import numpy as np
import vtk
from paraview.util.vtkAlgorithm import *
from vtkmodules.numpy_interface import dataset_adapter as dsa
from vtkmodules.vtkCommonDataModel import vtkExplicitStructuredGrid
@smproxy.source(name="ExplicitGrid_refactor",
label="TestExplicitGrid")
class PythonESGReader(VTKPythonAlgorithmBase):
def __init__ (self):
VTKPythonAlgorithmBase. __init__ (self, nInputPorts=0, nOutputPorts=1, outputType='vtkExplicitStructuredGrid')
self.__N = 3
def RequestInformation(self, request, inInfoVec, outInfoVec):
executive = self.GetExecutive()
outInfo = executive.GetOutputInformation(0)
outInfo.Set(executive.WHOLE_EXTENT(), 0, self. __N-1, 0, self.__ N-1, 0, self.__N-1)
return 1
def RequestData(self, request, inInfoVec, outInfoVec):
extent = (0, self. __N-1, 0, self.__ N-1, 0, self.__N-1)
nx = extent[1] - extent[0]
ny = extent[3] - extent[2]
nz = extent[5] - extent[4]
expected_cells = nx * ny * nz
output = dsa.WrapDataObject(
vtkExplicitStructuredGrid.GetData(outInfoVec, 0)
)
output.SetExtent(*extent)
newPoints = vtk.vtkPoints()
newPoints.Allocate(expected_cells * 8)
for k in range(nx):
for j in range(ny):
for i in range(nz):
# in each direction, shift the second cell
dx, dy, dz = 0.0, 0.0, 0.0
if i > 0:
dx = 0.2
if j > 0:
dy = 0.2
if k > 0:
dz = 0.2
# Add eight points
newPoints.InsertNextPoint(i-0.5+dx, j-0.5+dy, k-0.5+dz)
newPoints.InsertNextPoint(i+0.5+dx, j-0.5+dy, k-0.5+dz)
newPoints.InsertNextPoint(i-0.5+dx, j+0.5+dy, k-0.5+dz)
newPoints.InsertNextPoint(i+0.5+dx, j+0.5+dy, k-0.5+dz)
newPoints.InsertNextPoint(i-0.5+dx, j-0.5+dy, k+0.5+dz)
newPoints.InsertNextPoint(i+0.5+dx, j-0.5+dy, k+0.5+dz)
newPoints.InsertNextPoint(i-0.5+dx, j+0.5+dy, k+0.5+dz)
newPoints.InsertNextPoint(i+0.5+dx, j+0.5+dy, k+0.5+dz)
output.SetPoints(newPoints)
return 1
```
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 18, 2019, 11:12am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/10 "2019-12-18T11:12:06Z")
By default Glyph does not show all the points. Switch to “All Points” property.
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 18, 2019, 11:32am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/11 "2019-12-18T11:32:00Z")
Nice! That assures me that the points are correctly defined, now I can see all of them.
But still no cells.
Do I misunderstand the concept of implicit topology here? The code adds eight points at a time for each cell in the nested loops.
The code is very similar now to when I got vtkStructuredGrid to function properly, `output.SetPoints(newPoints)` corresponds to setting the grid/mesh in that case. With a different array of points then, only describing the coordinates of each common corner.
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 18, 2019, 11:55am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/12 "2019-12-18T11:55:27Z")
You should definitely be able to see the cells.
Can you show us a screenshot of the information tab ?
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 18, 2019, 12:06pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/13 "2019-12-18T12:06:12Z")
Sure thing
Additional information. For some reason, I see that ParaView crashes for me if I change the `Outline -> Surface With Edges` now. I didn’t experience this earlier I think (when I was missing some glyphs).
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 18, 2019, 12:17pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/14 "2019-12-18T12:17:36Z")
What do you see when you switch to Surface ?
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 18, 2019, 12:28pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/15 "2019-12-18T12:28:15Z")
Also a crash.
I can prevent ParaView from crashing by adding a loop
```auto
for i in range(expected_cells):
output.BlankCell(i)
```
But no surface (maybe expected).
If I add a loop
```auto
for i in range(expected_cells):
output.UnBlankCell(i)
```
at the end, ParaView crashes again.
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 18, 2019, 12:45pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/16 "2019-12-18T12:45:52Z")
Does ParaView crash if you add a ExplicitGridToUnstructuredGridFilter ?
And then if you add a UnstructuredGridToExplicitGridFilter ?
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 18, 2019, 12:53pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/17 "2019-12-18T12:53:40Z")
Does not seem to crash when applying
ExplicitStructuredGridToUnstructuredGrid,
followed by an
UnstructuredGridToExplicitStructuredGrid.
Still nothing shows
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 18, 2019, 1:43pm UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/18 "2019-12-18T13:43:36Z")
Can you save the result of ExplicitStructuredGridToUnstructuredGrid as a .vtu and send it here ?
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### Author:  [@MoS2](https://discourse.paraview.org/u/MoS2)
#### Post date: [December 19, 2019, 7:04am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/19 "2019-12-19T07:04:50Z")
Sure thing
[eight\_cells\_ExplicitStructuredGrid\_to\_Unstructured.vtu](https://discourse.paraview.org/uploads/short-url/1rCOAlEthgSxADB8P6hZbss306Q.vtu) (5.0 KB)
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 19, 2019, 9:27am UTC](https://discourse.paraview.org/t/how-to-define-a-vtkexplicitstructuredgrid/3189/20 "2019-12-19T09:27:46Z")
The cells are indeed incorrect and they all uses a single point.
You will have to compare your code with the one I sent before in order to figure out what is going on here.