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。
image.png
源码 见 1092.html ，对应的 官网示例
核心技术点：
使用proj4定义坐标系
使用新的坐标系生成新的view，将新view应用到map上
<!DOCTYPE html>
<html>
<head>
<title></title>
<link rel="stylesheet" href="../include/ol.css" type="text/css" />
<script src="../include/ol.js"></script>
</head>
<style></style>
<body>
<form class="form-inline">
<label for="epsg-query">搜索投影坐标系:</label>
<input type="text" id="epsg-query" placeholder="4326, 27700, US National Atlas, Swiss, France, ..."
class="form-control" size="50" />
<button id="epsg-search" class="btn">搜索</button>
<span id="epsg-result"></span>
<div>
<label for="render-edges">
渲染重投影区域边缘
<input type="checkbox" id="render-edges">
</label>
</div>
</form>
<div id="map" class="map"></div>
<div id="info"> </div>
<script>
var map = new ol.Map({
layers: [
new ol.layer.Tile({
source: new ol.source.OSM()
})
],
target: 'map',
view: new ol.View({
projection: 'EPSG:3857',
center: [0, 0],
zoom: 1
})
});
var queryInput = document.getElementById('epsg-query');
var searchButton = document.getElementById('epsg-search');
var resultSpan = document.getElementById('epsg-result');
var renderEdgesCheckbox = document.getElementById('render-edges');
function setProjection(code, name, proj4def, bbox) {
if (code === null || name === null || proj4def === null || bbox === null) {
resultSpan.innerHTML = 'Nothing usable found, using EPSG:3857...';
map.setView(new ol.View({
projection: 'EPSG:3857',
center: [0, 0],
zoom: 1
}));
return;
}
resultSpan.innerHTML = '(' + code + ') ' + name;
var newProjCode = 'EPSG:' + code;
proj4.defs(newProjCode, proj4def);
ol.proj.proj4.register(proj4);
var newProj = ol.proj.get(newProjCode);
var fromLonLat = ol.proj.getTransform('EPSG:4326', newProj);
// very approximate calculation of projection extent
var extent = ol.extent.applyTransform(
[bbox[1], bbox[2], bbox[3], bbox[0]], fromLonLat);
newProj.setExtent(extent);
var newView = new ol.View({
projection: newProj
});
map.setView(newView);
newView.fit(extent);
}
function search(query) {
resultSpan.innerHTML = 'Searching ...';
fetch('https://epsg.io/?format=json&q=' + query).then(function (response) {
return response.json();
}).then(function (json) {
var results = json['results'];
if (results && results.length > 0) {
for (var i = 0, ii = results.length; i < ii; i++) {
var result = results[i];
if (result) {
var code = result['code'];
var name = result['name'];
var proj4def = result['proj4'];
var bbox = result['bbox'];
if (code && code.length > 0 && proj4def && proj4def.length > 0 &&
bbox && bbox.length == 4) {
setProjection(code, name, proj4def, bbox);
return;
}
}
}
}
setProjection(null, null, null, null);
});
}
searchButton.onclick = function (event) {
search(queryInput.value);
event.preventDefault();
};
renderEdgesCheckbox.onchange = function () {
map.getLayers().forEach(function (layer) {
if (layer instanceof ol.layer.Tile) {
var source = layer.getSource();
if (source instanceof ol.source.TileImage) {
source.setRenderReprojectionEdges(renderEdgesCheckbox.checked);
}
}
});
};
</script>
</body>
</html>
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