title: plot data stored in a file using (mayavi) mlab.contour3d?
body: <p>I am struggling to do a simple contour3d plot in mayavi using data that is read in from a file. The data is a regular 3d cartesian grid in the form  </p>
  
  <pre><code>   x1   y1    z1    val(x1,y1,z1)  
     x1   y1    z2    val(x1,y1,z2)  
      .    .     .       .  
     x1   y1     z_K  val(x1,y1,z_K)  
  
     x1   y2     z1    val(x1,y2,z1)  
      .    .     .       .  
      .    .     .       .  
     x_L   y_M    z_K    val(x_L,y_M,z_K)  
  </code></pre>
  
  <p>(Here the first 3 values on each row give the (x,y,z) coordinates of the point while the 4th value gives the value of a scalar at that point.  I can paste a minimal example file if useful)  </p>
  
  <p><strong>The data file can be successfully read in using numpy.loadtxt , but how do I get from there
  to plotting an isosurface using (mayavi) mlab.contour3d</strong> ? I think the default output 
  array from loadtxt is not in the right format for mlab.contour3d.  </p>
  
  <p>All the examples I have been able to find of mlab.contour3d  generate a grid using ogrid, then plot a simple function (sin etc) of this grid. I have been able to run those examples successfully, but they don't tell me how to read in data from a file into the right format
  of array ready for plotting. I am sure it would help a great many newbies in a similar position if someone could give me a pointer ; plotting 3d data stored in a file generated by another program must surely be one of the most common plotting tasks scientists have to do.</p>