Question

I’m trying to fill in a structured grid with an analytical field, but despite reading the vtk docs, I haven’t found out how to actually set scalar values at the grid points or the set the spacing/origin info of the grid. Starting from the code below, how do I

1. associate spatial information with the grid (ie cell 0,0,0 is at coordinates 0,0,0, the spacing is dx in every direction)
2. associate scalar values with each grid point. To start, I just need one, but eventually I’d like to store 3 pieces of data at each point (not a vector, 3 distinct scalars).

grid = vtk.vtkStructuredGrid()
numPoints = int((maxGrid - minGrid)/dx)
grid.SetDimensions(numPoints, numPoints, numPoints)

Answer 1

In VTK there are 3 types of "structured" grids, vtkImageData (vtkUniformGrid derives from this), vtkRectilinearGrid, and vtkStructuredGrid. They are all structured in the sense that the topology is set. vtkImageData has constant spacing between points and is axis aligned, vtkRectilinearGrid is axis aligned but can vary the spacing in each axis direction, and vtkStructuredGrid has arbitrarily located points (cells may not be valid though).

For what you want to do you should do:

from vtk import *
dx = 2.0
grid = vtkImageData()
grid.SetOrigin(0, 0, 0) # default values
grid.SetSpacing(dx, dx, dx)
grid.SetDimensions(5, 8, 10) # number of points in each direction
# print grid.GetNumberOfPoints()
# print grid.GetNumberOfCells()
array = vtkDoubleArray()
array.SetNumberOfComponents(1) # this is 3 for a vector
array.SetNumberOfTuples(grid.GetNumberOfPoints())
for i in range(grid.GetNumberOfPoints()):
    array.SetValue(i, 1)

grid.GetPointData().AddArray(array)
# print grid.GetPointData().GetNumberOfArrays()
array.SetName("unit array")