openlayers3 聚合分析專題圖 cluster

 在地圖上查詢結果通常以標記點的形式展現，但是如果標記點較多，不僅會大大增加客戶端的渲染時間，讓客戶端變得很卡，而且會讓人產生密集恐懼症，為了解決這一問題，我們需要一種手段能在用戶有限的可視區域范圍內，利用最小的區域展示出最全面的信息，而又不產生重疊覆蓋。具體算法探討：點擊打開鏈接

openlayers3提供api具體實例使用方法:

  一.簡單實例：點擊打開鏈接

1.創建feature，添加到ol.source.Cluster 中；設置聚合半徑distance紅色標注

var count = 20000;

 var features = new Array(count); var e = 4500000; for (var i = 0; i < count; ++i) { var coordinates = [2 * e * Math.random() - e, 2 * e * Math.random() - e]; features[i] = new ol.Feature(new ol.geom.Point(coordinates)); } var source = new ol.source.Vector({ features: features }); var clusterSource = new ol.source.Cluster({ distance: parseInt(distance.value, 10), source: source });

2.添加到ol.layer.Vector圖層中，並根據feature屬性設置對應style

var styleCache = {}; var clusters = new ol.layer.Vector({ source: clusterSource, style: function(feature) { var size = feature.get('features').length; var style = styleCache[size]; if (!style) { style = new ol.style.Style({ image: new ol.style.Circle({ radius: 10, stroke: new ol.style.Stroke({ color: '#fff' }), fill: new ol.style.Fill({ color: '#3399CC' }) }), text: new ol.style.Text({ text: size.toString(), fill: new ol.style.Fill({ color: '#fff' }) }) }); styleCache[size] = style; } return style; } });

3.添加到map中即可

 var map = new ol.Map({ layers: [raster, clusters], target: 'map', view: new ol.View({ center: [0, 0], zoom: 2 }) });

二.實際應用 EarthQuake

1.初始化聚合圖層，設置distance，綁定縮放事件

 vector = new ol.layer.Vector({
        source: new ol.source.Cluster({
          distance: 40,
          source: new ol.source.Vector({
            url: 'https://openlayers.org/en/v4.2.0/examples/data/kml/2012_Earthquakes_Mag5.kml',
            format: new ol.format.KML({
              extractStyles: false
            })
          })
        }),
        style: styleFunction
      });




2.根據當前縮放resolution，及feature屬性設置渲染style

var currentResolution; function styleFunction(feature, resolution) { if (resolution != currentResolution) { calculateClusterInfo(resolution); currentResolution = resolution; } var style; var size = feature.get('features').length; if (size > 1) { style = new ol.style.Style({ image: new ol.style.Circle({ radius: feature.get('radius'), 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 { var originalFeature = feature.get('features')[0]; style = createEarthquakeStyle(originalFeature); } return style; }

3.根據點擊聚合圖形，設置渲染style

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)); } return styles; }

4.添加聚合圖層，並綁定點擊事件

 var map = new ol.Map({ layers: [raster, vector], interactions: ol.interaction.defaults().extend([new ol.interaction.Select({  condition: function(evt) { return evt.originalEvent.type == 'mousemove' || evt.type == 'singleclick'; }, style: selectStyleFunction })]), target: 'map', view: new ol.View({ center: [0, 0], zoom: 2 }) });