function replaceUnavailable(value){
  if(value===0) return 0;
  if(value == null || value == NaN || value == "") return "n/a";
  else return value;
}

function generate_custom_overlaygroup(){
  if(!Array.isArray() || OverlayConfig.length >=1){
    console.log("No valid overlay config present.");
    return null;
  }
  
  return new ol.layer.Group({
    combine: false,
    title: 'Custom Information',
    zIndex: layerSetZIndexBase['clientoverlay'],
    layers : map(OverlayConfig, function(current_overlay){
      
      console.log(current_overlay);
      return new ol.layer.Tile({
            title: 'Ground Infrastructure',
            type: 'tiles',
            opacity: 0.9,
            visible:true,
            extent: ol.proj.transformExtent([12.576354, 41.786571, 12.609483, 41.813856], 'EPSG:4326', 'EPSG:3857'),
            zIndex: layerSetZIndexBase['clientoverlay']+1,
            useInterimTilesOnError:false,
            source: new ol.source.XYZ({
                url: "/overlays/CIA/Ground Infrastructure/{z}/{x}/{-y}.png",
                tilePixelRatio: 1.000000,
                minZoom: 13,
                maxZoom: 18
            }),
            maxResolution: Math.min(
                ol.Sphere.getDistance(
                    [ground_infra_overlay_extent[0], ground_infra_overlay_extent[1]],
                    [ground_infra_overlay_extent[2], ground_infra_overlay_extent[1]]
                ),
                ol.Sphere.getDistance(
                    [ground_infra_overlay_extent[0], ground_infra_overlay_extent[1]],
                    [ground_infra_overlay_extent[0], ground_infra_overlay_extent[3]]
                )
            )
      }); // end return tile
    }) // end map
    
  });
  

}

// https://stackoverflow.com/questions/26246601/wildcard-string-comparison-in-javascript
// check if str matches against rule (e.g. whether D-ABCD matched D-*)
function matchRuleShort(str, rule) {
  var escapeRegex = (str) => str.replace(/([.*+?^=!:${}()|\[\]\/\\])/g, "\\$1");
  return new RegExp("^" + rule.split("*").map(escapeRegex).join(".*") + "$").test(str);
}