openlayers4 入门开发系列之前端动态渲染克里金插值 kriging 篇（附源码下载）

前言

openlayers4 官网的 api 文档介绍地址 openlayers4 api，里面详细的介绍 openlayers4 各个类的介绍，还有就是在线例子：openlayers4 官网在线例子，这个也是学习 openlayers4 的好素材。

openlayers4 入门开发系列的地图服务基于 Geoserver 发布的，关于 Geoserver 方面操作的博客，可以参考以下几篇文章：

• geoserver 安装部署步骤
• geoserver 发布地图服务 WMS
• geoserver 发布地图服务 WMTS
• geoserver 集成以及部署 arcgis server 瓦片数据

内容概览

1.基于 openlayers4 实现前端动态渲染克里金插值 kriging 效果
2.源代码 demo 下载

本篇的重点内容是利用 openlayers4 实现前端动态渲染克里金插值 kriging 功能，根据配置颜色模型不同渲染效果不同：

1. 颜色数组配置颜色带少，不够圆滑效果
   

2. 颜色数组配置颜色带多，比较圆滑效果
   

实现思路

• 利用开源 js 库克里金插值 kriging.js，源码 github 见这里：github；
  关于 kriging.js 的相关介绍详情说明，自行看 github 以及结合百度搜索。
• kriging.js 插值需要插值点，包括点坐标以及插值权重字段值，还需要插值范围边界，我这里的模拟插值点以及插值边界分别存储在 point.js 以及 world.js 文件。

point.js：

var points = [
{
"attributes": {
"FID": 0,
"NAME": "绵竹镇",
"TN_": 25.6
},
"geometry": {
"x": 103.6905556,
"y": 29.62972222
}
},
{
"attributes": {
"FID": 1,
"NAME": "高桥镇",
"TN_": 22.9
},
"geometry": {
"x": 103.4222222,
"y": 29.52638889
}
},
……省略号
]

world.js :

var world = [
[
[
104.13092800000004,
29.022763000000054
],
[
104.11851800000005,
28.966904000000056
],
[
104.10646800000006,
28.953798000000063
],
[
104.08176800000007,
28.958551000000057
],
[
104.07084300000008,
28.941115000000025
],
……省略号
]
]

• kriging.js 核心三个函数：

1. kriging.train

• var variogram=kriging.train(t,x,y,params.krigingModel,params.krigingSigma2,params.krigingAlpha);

1. kriging.grid

• var grid=kriging.grid(world,variogram,(extent[2]-extent[0])/200);

1. kriging.plot

• //使用分层设色渲染
• kriging.plot(canvas,grid,[extent[0],extent[2]],[extent[1],extent[3]],params.colors);

下面详细介绍上述函数用到的参数值：

1. params 常量配置值：

var params={
krigingModel:'exponential',//model还可选'gaussian','spherical'
krigingSigma2:0,
krigingAlpha:100,
canvasAlpha:0.9,//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"]
//colors:["#006837", "#1a9850", "#66bd63", "#a6d96a", "#d9ef8b", "#ffffbf","#fee08b", "#fdae61", "#f46d43", "#d73027", "#a50026"]
};

1. 读取插值点数据源，动态构造 kriging.js 插值参数t，x， y值：

var i, j, k, n ;
n = points.length;
var t = Array(n);
var x = Array(n);
var y = Array(n);
for(i = 0;i < n ; i++){
t[i] = points[i].attributes.TN_;
x[i] = points[i].geometry.x;
y[i] = points[i].geometry.y;
var feature = new ol.Feature({
geometry: new ol.geom.Point(ol.proj.transform([x[i], y[i]], 'EPSG:4326', 'EPSG:4326')),
value: t[i]
});
feature.setStyle(new ol.style.Style({
image: new ol.style.Circle({
radius: 6,
fill: new ol.style.Fill({color: "#00F"})
})
}));
WFSVectorSource.addFeature(feature);
}

更多的详情见：GIS之家小专栏

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