var map;
function init(){
var options = {
    projection: new OpenLayers.Projection("EPSG:3857"),
    units: "m",
    maxResolution: 78271.516953,
    maxExtent: new OpenLayers.Bounds(-20037508.34, -20037508.34,
                                     20037508.34, 20037508.34)
};

map = new OpenLayers.Map('map', options);


    var wms_sec = new OpenLayers.Layer.WMS( "Sectional Charts",
        "http://wms.chartbundle.com/wms",
        {layers: 'sec'} );
        var wms_tac = new OpenLayers.Layer.WMS( "Terminal Area Charts",
        "http://wms.chartbundle.com/wms",
        {layers: 'tac'});
        var wms_wac = new OpenLayers.Layer.WMS( "World Aeronautical Charts",
        "http://wms.chartbundle.com/wms",
        {layers: 'wac'});

       var wms_enrl = new OpenLayers.Layer.WMS( "IFR Enroute Low Charts",
        "http://wms.chartbundle.com/wms",
        {layers: 'enrl'});

      var wms_enra = new OpenLayers.Layer.WMS( "IFR Area Charts",
        "http://wms.chartbundle.com/wms",
        {layers: 'enra'});

      var wms_enrh = new OpenLayers.Layer.WMS( "IFR Enroute High Charts",
        "http://wms.chartbundle.com/wms",
        {layers: 'enrh'});

    var wms_secgrids = new OpenLayers.Layer.WMS( "Sectional Charts with Grid",
        "http://wms.chartbundle.com/wms",
        {layers: 'secgrids'} );
    var wms_tacgrids = new OpenLayers.Layer.WMS( "Terminal Area Charts with Grid",
        "http://wms.chartbundle.com/wms",
        {layers: 'tacgrids'} );

        var wms_wacgrids = new OpenLayers.Layer.WMS( "World Aeronautical Charts with Grid",
        "http://wms.chartbundle.com/wms",
        {layers: 'wacgrids'});

    map.addLayers([wms_sec, wms_tac, wms_wac, wms_enrl, wms_enra, wms_enrh, wms_secgrids, wms_tacgrids,wms_wacgrids]);
    map.addControl(new OpenLayers.Control.LayerSwitcher());
    var proj = new OpenLayers.Projection("EPSG:4326");
    var point = new OpenLayers.LonLat(-97, 38);
    map.setCenter(point.transform(proj, map.getProjectionObject()),3);
}