Changes

With a bit of zooming, clicking on <code>File -> Save image</code> in the <code>Surface</code> window, <code>allowing rendering</code>, and outputting to a large TIFF file, <code>save current</code>, then <code>apply</code>.

Note that for a good resolution plot, you will need many more increments. Using the lower and upper dx.map arguments will be useful to zoom into the space.