Openlayers利用kriging.js实现纯前端插值

关于空间插值这一块，也是GIS一个重要的分析。前端可以通过turf.js后端可以采用contour，如果仅有少量数据需要进行插值分析并进行展示，那应当如何做？可以采用turf.js但是turf.js插值效果是真的烂。通过检索发现可以通过kriging.js去做。kriging.js是基于canvas实现的在OL中可以通过imagecanvas来实现。

一、关于kriging.js
1、GitHub地址（https://github.com/oeo4b/kriging.js）
2、核心功能

kriging.train(t, x, y, model, sigma2, alpha):使用gaussian、exponential或spherical模型对数据集进行训练，返回的是一个variogram对象；
kriging.grid(polygons,variogram,width);使用刚才的variogram对象使polygons描述的地理位置内的格网元素具备不一样的预测值；
kriging.plot(canvas,grid,xlim,ylim,colors);将得到的格网grid渲染至canvas上。
二、效果图

在这里插入图片描述
三、demo示例

<!DOCTYPE html>
<html>
<head><meta charset="utf-8" /><title>前端空间插值</title><style>#map {height: 100%;width: 100%;}</style><link href="../script/ol4/ol.css" rel="stylesheet" /><script src="../script/ol4/ol.js"></script><script src="../script/kriging.js-master/data.js"></script><script src="../script/kriging.js-master/kriging.js"></script>
</head>
<body><div id="map"></div><script type="text/javascript">let params = {mapCenter: [116.40, 39.90],krigingModel: 'exponential',//model还可选'gaussian','spherical'krigingSigma2: 0,krigingAlpha: 226,canvasAlpha: 0.75,//canvas图层透明度colors: ["#00A600", "#01A600", "#03A700", "#04A700", "#05A800", "#07A800", "#08A900", "#09A900", "#0BAA00", "#0CAA00", "#0DAB00", "#0FAB00", "#10AC00", "#12AC00", "#13AD00", "#14AD00", "#16AE00", "#17AE00", "#19AF00", "#1AAF00", "#1CB000", "#1DB000", "#1FB100", "#20B100", "#22B200", "#23B200", "#25B300", "#26B300", "#28B400", "#29B400", "#2BB500", "#2CB500", "#2EB600", "#2FB600", "#31B700", "#33B700", "#34B800", "#36B800", "#37B900", "#39B900", "#3BBA00", "#3CBA00", "#3EBB00", "#3FBB00", "#41BC00", "#43BC00", "#44BD00", "#46BD00", "#48BE00", "#49BE00", "#4BBF00", "#4DBF00", "#4FC000", "#50C000", "#52C100", "#54C100", "#55C200", "#57C200", "#59C300", "#5BC300", "#5DC400", "#5EC400", "#60C500", "#62C500", "#64C600", "#66C600", "#67C700", "#69C700", "#6BC800", "#6DC800", "#6FC900", "#71C900", "#72CA00", "#74CA00", "#76CB00", "#78CB00", "#7ACC00", "#7CCC00", "#7ECD00", "#80CD00", "#82CE00", "#84CE00", "#86CF00", "#88CF00", "#8AD000", "#8BD000", "#8DD100", "#8FD100", "#91D200", "#93D200", "#95D300", "#97D300", "#9AD400", "#9CD400", "#9ED500", "#A0D500", "#A2D600", "#A4D600", "#A6D700", "#A8D700", "#AAD800", "#ACD800", "#AED900", "#B0D900", "#B2DA00", "#B5DA00", "#B7DB00", "#B9DB00", "#BBDC00", "#BDDC00", "#BFDD00", "#C2DD00", "#C4DE00", "#C6DE00", "#C8DF00", "#CADF00", "#CDE000", "#CFE000", "#D1E100", "#D3E100", "#D6E200", "#D8E200", "#DAE300", "#DCE300", "#DFE400", "#E1E400", "#E3E500", "#E6E600", "#E6E402", "#E6E204", "#E6E105", "#E6DF07", "#E6DD09", "#E6DC0B", "#E6DA0D", "#E6D90E", "#E6D710", "#E6D612", "#E7D414", "#E7D316", "#E7D217", "#E7D019", "#E7CF1B", "#E7CE1D", "#E7CD1F", "#E7CB21", "#E7CA22", "#E7C924", "#E8C826", "#E8C728", "#E8C62A", "#E8C52B", "#E8C42D", "#E8C32F", "#E8C231", "#E8C133", "#E8C035", "#E8BF36", "#E9BE38", "#E9BD3A", "#E9BC3C", "#E9BB3E", "#E9BB40", "#E9BA42", "#E9B943", "#E9B945", "#E9B847", "#E9B749", "#EAB74B", "#EAB64D", "#EAB64F", "#EAB550", "#EAB552", "#EAB454", "#EAB456", "#EAB358", "#EAB35A", "#EAB35C", "#EBB25D", "#EBB25F", "#EBB261", "#EBB263", "#EBB165", "#EBB167", "#EBB169", "#EBB16B", "#EBB16C", "#EBB16E", "#ECB170", "#ECB172", "#ECB174", "#ECB176", "#ECB178", "#ECB17A", "#ECB17C", "#ECB17E", "#ECB27F", "#ECB281", "#EDB283", "#EDB285", "#EDB387", "#EDB389", "#EDB38B", "#EDB48D", "#EDB48F", "#EDB591", "#EDB593", "#EDB694", "#EEB696", "#EEB798", "#EEB89A", "#EEB89C", "#EEB99E", "#EEBAA0", "#EEBAA2", "#EEBBA4", "#EEBCA6", "#EEBDA8", "#EFBEAA", "#EFBEAC", "#EFBFAD", "#EFC0AF", "#EFC1B1", "#EFC2B3", "#EFC3B5", "#EFC4B7", "#EFC5B9", "#EFC7BB", "#F0C8BD", "#F0C9BF", "#F0CAC1", "#F0CBC3", "#F0CDC5", "#F0CEC7", "#F0CFC9", "#F0D1CB", "#F0D2CD", "#F0D3CF", "#F1D5D1", "#F1D6D3", "#F1D8D5", "#F1D9D7", "#F1DBD8", "#F1DDDA", "#F1DEDC", "#F1E0DE", "#F1E2E0", "#F1E3E2", "#F2E5E4", "#F2E7E6", "#F2E9E8", "#F2EBEA", "#F2ECEC", "#F2EEEE", "#F2F0F0", "#F2F2F2"]};let baseLayer = new ol.layer.Tile({title: "base",source: new ol.source.OSM()});let map = new ol.Map({target: 'map',layers: [baseLayer],view: new ol.View({center: params.mapCenter,projection: 'EPSG:4326',zoom: 8})});let WFSVectorSource = new ol.source.Vector();let WFSVectorLayer = new ol.layer.Vector({source: WFSVectorSource,});map.addLayer(WFSVectorLayer);//创建要素for (let i = 0; i < data.features.length; i++) {let feature = new ol.Feature({geometry: new ol.geom.Point([data.features[i].attributes.x, data.features[i].attributes.y]),value: data.features[i].attributes.z});feature.setStyle(new ol.style.Style({image: new ol.style.Circle({radius: 6,fill: new ol.style.Fill({ color: "#00F" })})}));WFSVectorSource.addFeature(feature);}//定义裁剪边界let coord = [[[117.315375, 40.181212],[117.367916, 40.135762],[116.751758, 40.002595],[116.754136, 39.870341],[116.913383, 39.804999],[116.901858, 39.680614],[116.788145, 39.56255],[116.535646, 39.590346],[116.392103, 39.491124],[116.4293, 39.433841],[116.387072, 39.417336],[116.237232, 39.476253],[116.172242, 39.578854],[115.728745, 39.479123],[115.610225, 39.588658],[115.508537, 39.59137],[115.416399, 39.733407],[115.416624, 39.776734],[115.550565, 39.772964],[115.408433, 40.015829],[115.85422, 40.144999],[115.922315, 40.216777],[115.708758, 40.499032],[115.89819, 40.585919],[116.03778, 40.577909],[116.208725, 40.741562],[116.454984, 40.739689],[116.297615, 40.910402],[116.43816, 40.870116],[116.405424, 40.94854],[116.537137, 40.9661],[116.621495, 41.057333],[116.703349, 40.853574],[116.93405, 40.675155],[117.454502, 40.647216],[117.387854, 40.533274],[117.166811, 40.503979],[117.164198, 40.373887],[117.315375, 40.181212]]];       let clipgeom = new ol.geom.Polygon(coord);            //绘制kriging插值图let canvasLayer = null;let drawKriging =function (extent){let values = [], lngs = [], lats = [];WFSVectorSource.forEachFeature(function (feature) {values.push(feature.getProperties().value);lngs.push(feature.getGeometry().getCoordinates()[0]);lats.push(feature.getGeometry().getCoordinates()[1]);})console.log(values.length)if (values.length > 3) {let letiogram = kriging.train(values, lngs, lats,params.krigingModel, params.krigingSigma2, params.krigingAlpha);let ex = clipgeom.getExtent();let grid = kriging.grid(coord, letiogram, (ex[2] - ex[0]) / 200);               //移除已有图层if (canvasLayer !== null) {map.removeLayer(canvasLayer);}//创建新图层canvasLayer = new ol.layer.Image({source: new ol.source.ImageCanvas({canvasFunction: (extent, resolution, pixelRatio, size, projection) => {console.log(extent);let canvas = document.createElement('canvas');canvas.width = size[0];canvas.height = size[1];canvas.style.display = 'block';//设置canvas透明度canvas.getContext('2d').globalAlpha = params.canvasAlpha;//使用分层设色渲染kriging.plot(canvas, grid,[extent[0], extent[2]], [extent[1], extent[3]], params.colors);                            return canvas;},projection: 'EPSG:4326'})})             //向map添加图层map.addLayer(canvasLayer);} else {alert("有效样点个数不足，无法插值");}}      //首次加载，自动渲染一次差值图let extent = clipgeom.getExtent();drawKriging(extent);</script>
</body>
</html>

四、参考文章
1、https://www.jianshu.com/p/c8473ac0b08a
2、https://www.cnblogs.com/naaoveGIS/p/9444480.html
3、https://www.cnblogs.com/giserhome/p/10851799.html
4、https://mathiasleroy.com/georeferenced-dynamic-kriging/

五、data.js数据

var data={"features": [{"attributes": {"FID": 0,"id": 1,"name": "Beijing US Embassy","x": 116.468,"y": 39.954999999999998,"z": 46,"xu": 454558.72859999997,"yu": 4422898.159},"geometry": {"x": 116.468,"y": 39.954999999999998}},{"attributes": {"FID": 1,"id": 2,"name": "Temple of Heaven","x": 116.407,"y": 39.886000000000003,"z": 36,"xu": 449297.45990000002,"yu": 4415272.716},"geometry": {"x": 116.407,"y": 39.886000000000003}},{"attributes": {"FID": 2,"id": 3,"name": "Haidian Beijing Botanical Garden","x": 116.20699999999999,"y": 40.002000000000002,"z": 40,"xu": 432311.35320000001,"yu": 4428280.3169999998},"geometry": {"x": 116.20699999999999,"y": 40.002000000000002}},{"attributes": {"FID": 3,"id": 4,"name": "Chaoyang Olympic Sports Center116.397","x": 116.39700000000001,"y": 39.981999999999999,"z": 43,"xu": 448514.42090000003,"yu": 4425933.4840000002},"geometry": {"x": 116.39700000000001,"y": 39.981999999999999}},{"attributes": {"FID": 4,"id": 5,"name": "Chaoyang Agricultural Exhibition 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39.712000000000003}},{"attributes": {"FID": 14,"id": 18,"name": "Xianghe EPA","x": 117.009,"y": 39.765999999999998,"z": 204,"xu": 500770.85320000001,"yu": 4401786.0719999997},"geometry": {"x": 117.009,"y": 39.765999999999998}},{"attributes": {"FID": 15,"id": 19,"name": "Badaling Northwest","x": 115.988,"y": 40.365000000000002,"z": 46,"xu": 414076.95390000002,"yu": 4468761.409},"geometry": {"x": 115.988,"y": 40.365000000000002}},{"attributes": {"FID": 16,"id": 20,"name": "East Fourth Ring Road","x": 116.483,"y": 39.939,"z": 181,"xu": 455829.68479999999,"yu": 4421114.7860000003},"geometry": {"x": 116.483,"y": 39.939}},{"attributes": {"FID": 17,"id": 21,"name": "Yanqing town","x": 115.97199999999999,"y": 40.453000000000003,"z": 59,"xu": 412832.08510000003,"yu": 4478545.159},"geometry": {"x": 115.97199999999999,"y": 40.453000000000003}},{"attributes": {"FID": 18,"id": 22,"name": "Miyun Reservoir","x": 116.911,"y": 40.499000000000002,"z": 63,"xu": 492458.57429999998,"yu": 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}