Reprojection with EPSG.io Search

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Reprojection with EPSG.io Search

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.

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Reprojection with EPSG.io Search</title>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></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, US National Atlas, Swiss, France, ..." class="form-control" size="50" />
      <button id="epsg-search" class="btn">Search</button>
      <span id="epsg-result"></span>
      <div>
        <label for="render-edges">
          Render reprojection edges
          <input type="checkbox" id="render-edges">
        </label>
      </div>
    </form>
    <script src="index.js"></script>
  </body>
</html>

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index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import {applyTransform} from 'ol/extent';
import TileLayer from 'ol/layer/Tile';
import {get as getProjection, getTransform} from 'ol/proj';
import {register} from 'ol/proj/proj4';
import OSM from 'ol/source/OSM';
import TileImage from 'ol/source/TileImage';
import proj4 from 'proj4';


var map = new Map({
  layers: [
    new TileLayer({
      source: new OSM()
    })
  ],
  target: 'map',
  view: new 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 View({
      projection: 'EPSG:3857',
      center: [0, 0],
      zoom: 1
    }));
    return;
  }

  resultSpan.innerHTML = '(' + code + ') ' + name;

  var newProjCode = 'EPSG:' + code;
  proj4.defs(newProjCode, proj4def);
  register(proj4);
  var newProj = getProjection(newProjCode);
  var fromLonLat = getTransform('EPSG:4326', newProj);

  // very approximate calculation of projection extent
  var extent = applyTransform(
    [bbox[1], bbox[2], bbox[3], bbox[0]], fromLonLat);
  newProj.setExtent(extent);
  var 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) {
    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);
  });
}


/**
 * Handle click event.
 * @param {Event} event The event.
 */
searchButton.onclick = function(event) {
  search(queryInput.value);
  event.preventDefault();
};


/**
 * Handle change event.
 */
renderEdgesCheckbox.onchange = function() {
  map.getLayers().forEach(function(layer) {
    if (layer instanceof TileLayer) {
      var source = layer.getSource();
      if (source instanceof TileImage) {
        source.setRenderReprojectionEdges(renderEdgesCheckbox.checked);
      }
    }
  });
};

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package.json{
  "name": "reprojection-by-code",
  "dependencies": {
    "ol": "6.1.1",
    "proj4": "2.5.0"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}