code: private boolean isVisible(RuleInfo rule, ViewPort viewPort) {
  		if (rule == null) {
  			return true;
  		}
  		double minResolution = Double.MAX_VALUE;
  		double maxResolution = Double.MIN_VALUE;
  
  		if (rule.getMinScaleDenominator() != null && rule.getMinScaleDenominator().getMinScaleDenominator() != 0) {
  			maxResolution = viewPort.toResolution(rule.getMinScaleDenominator().getMinScaleDenominator());
  		}
  
  		if (rule.getMaxScaleDenominator() != null && rule.getMaxScaleDenominator().getMaxScaleDenominator() != 0) {
  			minResolution = viewPort.toResolution(rule.getMaxScaleDenominator().getMaxScaleDenominator());
  		}
  
  		return (maxResolution <= viewPort.getResolution() && viewPort.getResolution() < minResolution);
  	}
docs: TODO This method might be interesting as a static method in some SLD utility class.