本篇的重點內容是利用openlayers實現聚合圖功能，效果圖如下：

實現思路

• 介面設計

//聚合圖
"<div style='height:25px;background:#30A4D5;margin-top:25px;width: 98%;margin-left: 3px;'>" +
             "<span style='margin-left:5px;font-size: 13px;color:white;'>聚合圖</span>" +
        "</div>" +
       '<div id="tool-ol-ClusterLayer" style="padding:5px;">' +
            '<div style="float:left;">' +
            '<input type="checkbox" name="tool-ol-ClusterLayer" style="width: 15px;height: 15px;vertical-align: middle;margin: auto;"/>' +
            '<label style="font-weight: normal;vertical-align: middle;margin: auto;">聚合圖</label>' +
            '</div>' +
'</div>' 

• 點選事件

//載入聚合圖
$("#tool-ol-ClusterLayer input").bind("click", function () {
            if (this.checked) {
                if(!bxmap.olClusterLayer.isLoad){
                    bxmap.olClusterLayer.Init(bmap);
                }
                else{
                    bxmap.olClusterLayer.showClusterLayer();
                }
            }
            
 
else {
                bxmap.olClusterLayer.hideClusterLayer();
            }
})

• 初始化以及核心程式碼實現

var bxmap = bxmap || {};
bxmap.olClusterLayer = {
    map:null,
    isLoad:false,
    layer: null,//聚合圖圖層
    originalStyle:null,//聚合原始樣式
    selectStyleFunction:null,
    Init:function(bmap){
        
 
//載入聚合圖
        this.map = bmap.getMap();
        this.isLoad = true;
        //設定原始樣式
        this.originalStyle = new ol.style.Style({
            image: new ol.style.Circle({
                radius: 5,
                stroke: new ol.style.Stroke({
                    color: '#fff'
                }),
                fill: new ol.style.Fill({
                    color: '#3399CC'
                })
            })
        });
        this.initClusterLayer(qy);
    },
    /**
     * 初始化載入-聚合圖
     */
    initClusterLayer:function(data){
        var num = data.features.length;
        if (num > 0) {
            var features = new Array(num);
            for (var i = 0; i < num; i++) {
                var geo = data.features[i].geometry;
                var coordinate = [geo.x, geo.y];
                features[i] = new ol.Feature({
                    geometry: new ol.geom.Point(coordinate),
                    weight: data.features[i].attributes[field_dz]
                });
            }
            this.loadClusterLayer(features,this.originalStyle);
        }
    },
    /**
     * 建立聚合圖層
     * @method loadClusterLayer
     * @param  features 渲染聚合圖層的要素集
     * @param  originalStyle圖層的原始樣式style
     * @return null
     */
    loadClusterLayer:function (features, originalStyle) {
        var self = bxmap.olClusterLayer;
        var maxFeatureCount, currentResolution;
        var textFill = new ol.style.Fill({
            color: '#fff'
        });
        var textStroke = new ol.style.Stroke({
            color: 'rgba(0, 0, 0, 0.6)',
            width: 3
        });

        var invisibleFill = new ol.style.Fill({
            color: 'rgba(255, 255, 255, 0.01)'
        });
        var earthquakeFill = new ol.style.Fill({
            color: 'rgba(255, 153, 0, 0.8)'
        });
        var earthquakeStroke = new ol.style.Stroke({
            color: 'rgba(255, 204, 0, 0.2)',
            width: 1
        });
        function createEarthquakeStyle(feature, style) {
            return new ol.style.Style({
                geometry: feature.getGeometry(),
                image: new ol.style.Circle({
                    radius: 5,
                    stroke: new ol.style.Stroke({
                        color: '#fff'
                    }),
                    fill: new ol.style.Fill({
                        color: '#3399CC'
                    })
                })
            });
        }
        /*
         *選中樣式
        */
        function selectStyleFunction(feature) {
            var styles = [new ol.style.Style({
                image: new ol.style.Circle({
                    radius: feature.get('radius'),
                    fill: invisibleFill
                })
            })];
            var originalFeatures = feature.get('features');
            var originalFeature;
            for (var i = originalFeatures.length - 1; i >= 0; --i) {
                originalFeature = originalFeatures[i];
                styles.push(createEarthquakeStyle(originalFeature, originalStyle));
            }
            return styles;
        }
        /*
         *設定沒有聚合效果的原始樣式
         */
        function createOriginalStyle(feature) {
            return new ol.style.Style({
                image: new ol.style.Circle({
                    radius: 8,
                    stroke: new ol.style.Stroke({
                        color: '#fff'
                    }),
                    fill: new ol.style.Fill({
                        color: '#3399CC'
                    })
                })
            });
        }
        /*
         *計算每個聚合點的半徑大小
         */
        function calculateClusterInfo(resolution) {
            maxFeatureCount = 0;
            var features = self.layer.getSource().getFeatures();
            var feature, radius;
            for (var i = features.length - 1; i >= 0; --i) {
                feature = features[i];
                var originalFeatures = feature.get('features');
                var extent = ol.extent.createEmpty();
                var j, jj;
                for (j = 0, jj = originalFeatures.length; j < jj; ++j) {
                    ol.extent.extend(extent, originalFeatures[j].getGeometry().getExtent());
                }
                maxFeatureCount = Math.max(maxFeatureCount, jj);
                radius = 0.25 * (ol.extent.getWidth(extent) + ol.extent.getHeight(extent)) /
                    resolution;
                feature.set('radius', radius);
            }
        }
        /*
         *設定聚合樣式
         */
        function styleFunction(feature, resolution) {
            //計算每個聚合點的半徑大小
            if (resolution != currentResolution) {
                calculateClusterInfo(resolution);
                currentResolution = resolution;
            }
            var style;
            var size = feature.get('features').length;//每個點當前的聚合點數
            if (size > 1) {//設定聚合效果樣式
                style = new ol.style.Style({
                    image: new ol.style.Circle({
                        radius: feature.get('radius'),//獲取聚合圓圈的半徑大小，聚合的點數越多，圓圈的半徑越大
                        fill: new ol.style.Fill({
                            color: [255, 153, 0, Math.min(0.8, 0.4 + (size / maxFeatureCount))]
                        })
                    }),
                    text: new ol.style.Text({
                        text: size.toString(),
                        fill: textFill,
                        stroke: textStroke
                    })
                });
            } else {//設定沒有聚合效果的原始樣式
                style = originalStyle;
            }
            return style;
        }
        self.layer = new ol.layer.Vector({
            source: new ol.source.Cluster({//向量圖層的資料來源為聚合型別
                distance: 40,//聚合距離
                source: new ol.source.Vector({//聚合資料來源
                    features: features
                })
            }),
            style: styleFunction//聚合樣式
        });
        self.selectStyleFunction = selectStyleFunction;
        self.map.addLayer(self.layer);
        //縮放至範圍
        self.map.getView().setCenter([12637973.949997703, 2657176.0178779177]);
        self.map.getView().setZoom(10);
    },
    showClusterLayer:function(){
        var self = bxmap.olClusterLayer;
        if (self.layer) {
            self.layer.setVisible(true);
            //縮放至範圍
            self.map.getView().setCenter([12637973.949997703, 2657176.0178779177]);
            self.map.getView().setZoom(10);
        }
    },
    hideClusterLayer:function(){
        var self = bxmap.olClusterLayer;
        if (self.layer) {
            self.layer.setVisible(false);
        }
    }

}