四章-37-矢量标签的显示控制
2020-04-21 本文已影响0人
彩云飘过
本文基于腾讯课堂老胡的课《跟我学Openlayers--基础实例详解》做的学习笔记，使用的openlayers 5.3.x api。
源码 见 1037.html ，对应的 官网示例
image.png
<!DOCTYPE html>
<html>
<head>
<title>矢量标签显示控制</title>
<link rel="stylesheet" href="../include/ol.css" type="text/css" />
<script src="../include/ol.js"></script>
</head>
<body>
<div id="map" class="map"></div>
<script>
var map = new ol.Map({
target: "map",
view: new ol.View({
center: [0, 0],
zoom: 1
})
});
//文字标签样式
var labelStyle = new ol.style.Style({
geometry: function (feature) {
var geometry = feature.getGeometry();
//关键代码，找到最宽的多边形，然后显示字体标签
if (geometry.getType() == "MultiPolygon") {
// 多个多边形要素集合中仅渲染最宽的那个
var polygons = geometry.getPolygons();
var widest = 0;
for (var i = 0, ii = polygons.length; i < ii; ++i) {
var polygon = polygons[i];
var width = ol.extent.getWidth(polygon.getExtent());
if (width > widest) {
widest = width;
geometry = polygon;
}
}
}
return geometry;
},
text: new ol.style.Text({
font: "14px Calibri,sans-serif",
overflow: true,
fill: new ol.style.Fill({
color: "#000"
}),
stroke: new ol.style.Stroke({
color: "#fff",
width: 3
})
})
});
//国家边界样式
var countryStyle = new ol.style.Style({
fill: new ol.style.Fill({
color: "rgba(255, 255, 255, 0.6)"
}),
stroke: new ol.style.Stroke({
color: "#319FD3",
width: 1
})
});
var style = [countryStyle, labelStyle];
var vectorLayer = new ol.layer.Vector({
source: new ol.source.Vector({
url: "../data/lands.geojson",
format: new ol.format.GeoJSON()
}),
style: function (feature) {
labelStyle.getText().setText(feature.get("name"));
return style;
},
declutter: true
});
map.addLayer(vectorLayer);
</script>
</body>
</html>
