More Mapstraction filtering; this time showing and revealing map markers which are contained within a radius

JavaScript Demo Source: mxn-filter-radius.js

var mapstraction;
var centerRadius;

function initialize(api_provider_id)
 {
    // hide the right-hand filter handle
    $('handle2').hide();

    mapstraction = new mxn.Mapstraction('map', api_provider_id);
    mapstraction.enableScrollWheelZoom();
    myPoint = new mxn.LatLonPoint(52.250873, 0.110292);
    mapstraction.setCenterAndZoom(myPoint, 12);
    centerRadius = new mxn.Radius(myPoint, 20);
    addMarkers(50);
    addSlider();
    sliderChanged(1);
}

function addMarkers(count) {
    var bounds = mapstraction.getBounds();
    var sw = bounds.getSouthWest();
    var ne = bounds.getNorthEast();
    while (count--) {
        var ll = new mxn.LatLonPoint(sw.lat + ((ne.lat - sw.lat) * Math.random()),
        	sw.lon + ((ne.lon - sw.lon) * Math.random())
			);
        var marker = new mxn.Marker(ll);
        var distance = mxn.util.KMToMiles(marker.location.distance(myPoint));
        var el = "Distance: " + distance.toFixed(2) + " Mile(s)";
        marker.setInfoBubble(el);
        marker.setAttribute('distance', distance);
        mapstraction.addMarker(marker);
    }
}

function addSlider() {
    slider = new Control.Slider('handle1', 'track', {
        range: $R(0, 5, false),
        step: 1,
        restricted: true,
        sliderValue: 1,
        onChange: sliderChanged,
        onSlide: sliderChanged
    });
}

function sliderChanged(radius) {
    var foo = "x";
    mapstraction.removeAllPolylines();
    mapstraction.removeAllFilters();

    var sliderPoly = centerRadius.getPolyline(mxn.util.milesToKM(radius), '#00F');
    sliderPoly.setOpacity(0.5);
    mapstraction.addPolyline(sliderPoly);
    mapstraction.addFilter('distance', 'le', radius);
    var selectedCount = mapstraction.doFilter();
    var tw = document.getElementById('timeWindow');
    tw.innerHTML = 'Radius: ' + radius.toFixed(2) +
    ' Mile(s)
Selected Markers: ' + selectedCount;
}