docs: def create_graphics(self):
          """Create images related to this BAM file using GnuPlot."""
  
          rnftools.utils.shell('"{}" "{}"'.format("gnuplot", self._gp_fn))
  
          if self.render_pdf_method is not None:
              svg_fn = self._svg_fn
              pdf_fn = self._pdf_fn
              svg42pdf(svg_fn, pdf_fn, method=self.render_pdf_method)