Demonstrates client-side raster reprojection of OSM to arbitrary projection
This example shows client-side raster reprojection capabilities from OSM (EPSG:3857) to arbitrary projection by searching in EPSG.io database.
import 'ol/ol.css';
import Graticule from 'ol/layer/Graticule';
import Map from 'ol/Map';
import OSM from 'ol/source/OSM';
import Stroke from 'ol/style/Stroke';
import TileDebug from 'ol/source/TileDebug';
import TileLayer from 'ol/layer/Tile';
import View from 'ol/View';
import proj4 from 'proj4';
import {applyTransform} from 'ol/extent';
import {get as getProjection, getTransform} from 'ol/proj';
import {register} from 'ol/proj/proj4';
const osmSource = new OSM();
const debugLayer = new TileLayer({
source: new TileDebug({
tileGrid: osmSource.getTileGrid(),
projection: osmSource.getProjection(),
}),
visible: false,
});
const graticule = new Graticule({
// the style to use for the lines, optional.
strokeStyle: new Stroke({
color: 'rgba(255,120,0,0.9)',
width: 2,
lineDash: [0.5, 4],
}),
showLabels: true,
visible: false,
wrapX: false,
});
const map = new Map({
layers: [
new TileLayer({
source: osmSource,
}),
debugLayer,
graticule,
],
target: 'map',
view: new View({
projection: 'EPSG:3857',
center: [0, 0],
zoom: 1,
}),
});
const queryInput = document.getElementById('epsg-query');
const searchButton = document.getElementById('epsg-search');
const resultSpan = document.getElementById('epsg-result');
const renderEdgesCheckbox = document.getElementById('render-edges');
const showTilesCheckbox = document.getElementById('show-tiles');
const showGraticuleCheckbox = document.getElementById('show-graticule');
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 View({
projection: 'EPSG:3857',
center: [0, 0],
zoom: 1,
})
);
return;
}
resultSpan.innerHTML = '(' + code + ') ' + name;
const newProjCode = 'EPSG:' + code;
proj4.defs(newProjCode, proj4def);
register(proj4);
const newProj = getProjection(newProjCode);
const fromLonLat = getTransform('EPSG:4326', newProj);
let worldExtent = [bbox[1], bbox[2], bbox[3], bbox[0]];
newProj.setWorldExtent(worldExtent);
// approximate calculation of projection extent,
// checking if the world extent crosses the dateline
if (bbox[1] > bbox[3]) {
worldExtent = [bbox[1], bbox[2], bbox[3] + 360, bbox[0]];
}
const extent = applyTransform(worldExtent, fromLonLat, undefined, 8);
newProj.setExtent(extent);
const newView = new 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) {
const results = json['results'];
if (results && results.length > 0) {
for (let i = 0, ii = results.length; i < ii; i++) {
const result = results[i];
if (result) {
const code = result['code'];
const name = result['name'];
const proj4def = result['proj4'];
const 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);
});
}
/**
* Handle click event.
* @param {Event} event The event.
*/
searchButton.onclick = function (event) {
search(queryInput.value);
event.preventDefault();
};
/**
* Handle checkbox change events.
*/
renderEdgesCheckbox.onchange = function () {
osmSource.setRenderReprojectionEdges(renderEdgesCheckbox.checked);
};
showTilesCheckbox.onchange = function () {
debugLayer.setVisible(showTilesCheckbox.checked);
};
showGraticuleCheckbox.onchange = function () {
graticule.setVisible(showGraticuleCheckbox.checked);
};
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Reprojection with EPSG.io Search</title>
<!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
<script src="https://unpkg.com/elm-pep"></script>
<!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
<script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,URL,TextDecoder,Number.isInteger"></script>
<style>
.map {
width: 100%;
height:400px;
}
</style>
</head>
<body>
<div id="map" class="map"></div>
<form class="form-inline">
<label for="epsg-query">Search projection: </label>
<input type="text" id="epsg-query" placeholder="4326, 27700, 3031, US National Atlas, Swiss, France, ..." class="form-control" size="50" />
<button id="epsg-search" class="btn">Search</button>
<span id="epsg-result"></span>
</form>
<form class="form-inline">
<label for="render-edges">
Render reprojection edges:
<input type="checkbox" id="render-edges" />
</label>
<label for="show-tiles">
Show tile coordinates:
<input type="checkbox" id="show-tiles" />
</label>
<label for="show-graticule">
Show graticule:
<input type="checkbox" id="show-graticule" />
</label>
</form>
<script src="main.js"></script>
</body>
</html>
{
"name": "reprojection-by-code",
"dependencies": {
"ol": "6.6.1",
"proj4": "2.7.4"
},
"devDependencies": {
"parcel": "^2.0.0-beta.1"
},
"scripts": {
"start": "parcel index.html",
"build": "parcel build --public-url . index.html"
}
}