title: How to set data values on a vtkStructuredGrid
body: <p>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</p>
  
  <ol>
  <li>associate spatial information with the grid (ie cell 0,0,0 is at coordinates 0,0,0, the spacing is dx in every direction)</li>
  <li>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).</li>
  </ol>
  
  
  
  <pre><code>grid = vtk.vtkStructuredGrid()
  numPoints = int((maxGrid - minGrid)/dx)
  grid.SetDimensions(numPoints, numPoints, numPoints)
  </code></pre>