id cells
using <code><a href="binMean2D.html">binMean2D()</a></code>.  If <code>pregrid</code> is <code>TRUE</code> or
<code>4</code>, then this averaging is done within a grid that is 4 times finer
than the grid that will be used for the Barnes interpolation. Otherwise,
<code>pregrid</code> may be a single integer indicating the grid refinement (4
being the result if <code>TRUE</code> had been supplied), or a vector of two
integers, for the grid refinement in x and y. The purpose of using
<code>pregrid</co