概述
本文分享一个结合turf.js实现前端等值线的生成，并对结果做了圆滑处理，并在OL4中进行展示。
效果
圆滑前
圆滑后
实现
实现比较简单，源代码如下：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Measure</title>
<link rel="stylesheet" href="../../plugin/ol4/ol.css" type="text/css">
<script src="../../plugin/ol4/ol.js"></script>
<script src="../../plugin/turf/turf.js"></script>
<script type="text/javascript" src="../../plugin/jquery/jquery-3.1.1.min.js"></script>
<style>
html, body, #map{
margin: 0;
padding: 0;
overflow: hidden;
width: 100%;
height: 100%;
}
</style>
</head>
<body>
<div id="map" class="map"></div>
<script>
function styleFunction(feature) {
var tem = feature.get("temperature");
var colors = ["#5a9fdd", "#f7eb0c", "#fc9e10", "#f81e0d", "#aa2ab3"];
var color = colors[parseInt(tem/2)];
return new ol.style.Style({
fill: new ol.style.Fill({
color: color
}),
stroke: new ol.style.Stroke({
color: color,
width: 4
}),
image: new ol.style.Circle({
radius: 5,
fill: new ol.style.Fill({
color: color
}),
stroke: new ol.style.Stroke({
color: '#fff',
width: 1
})
})
});
}
// create a grid of points with random z-values in their properties
var extent = [0, 30, 20, 50];
var cellWidth = 100;
var pointGrid = turf.pointGrid(extent, cellWidth, {units: 'miles'});
for (var i = 0; i < pointGrid.features.length; i++) {
pointGrid.features[i].properties.temperature = Math.random() * 10;
}
var breaks = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var lines = turf.isolines(pointGrid, breaks, {zProperty: 'temperature'});
// var _lFeatures = lines.features;
// for(var i=0;i<_lFeatures.length;i++){
// var _coords = _lFeatures[i].geometry.coordinates;
// var _lCoords = [];
// for(var j=0;j<_coords.length;j++){
// var _coord = _coords[j];
// var line = turf.lineString(_coord);
// var curved = turf.bezierSpline(line);
// _lCoords.push(curved.geometry.coordinates);
// }
// _lFeatures[i].geometry.coordinates = _lCoords;
// }
var featureslines = (new ol.format.GeoJSON()).readFeatures(lines);
var features = (new ol.format.GeoJSON()).readFeatures(pointGrid);
features = features.concat(featureslines);
for(var i=0;i<features.length;i++){
features[i].getGeometry().transform("EPSG:4326","EPSG:3857");
}
var source = new ol.source.Vector({
features:features
});
var vector = new ol.layer.Vector({
source: source,
style: styleFunction
});
var map = new ol.Map({
layers: [getTdtLayer("img_w"), vector],
target: 'map',
view: new ol.View({
center: [12577713.642017495, 2971206.770222437],
zoom: 3
})
});
function getTdtLayer(lyr){
var url = "http://t0.tianditu.com/DataServer?T="+lyr+"&X={x}&Y={y}&L={z}";
var layer = new ol.layer.Tile({
source: new ol.source.XYZ({
url:url
})
});
return layer;
}
</script>
</body>
</html>
说明：
1.注释掉的代码为做圆滑处理的代码，拷贝请取消注释。
技术博客
CSDN：http://blog.csdn.NET/gisshixisheng
在线教程
https://edu.csdn.net/course/detail/799
https://edu.csdn.net/course/detail/7471
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