Question

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.

main.js

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);
};

index.html

<!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:&nbsp</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:&nbsp;
        <input type="checkbox" id="render-edges" />
      </label>
      &nbsp;&nbsp;&nbsp;&nbsp;
      <label for="show-tiles">
        Show tile coordinates:&nbsp;
        <input type="checkbox" id="show-tiles" />
      </label>
      &nbsp;&nbsp;&nbsp;&nbsp;
      <label for="show-graticule">
        Show graticule:&nbsp;
        <input type="checkbox" id="show-graticule" />
      </label>
    </form>
    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "reprojection-by-code",
  "dependencies": {
    "ol": "7.1.0",
    "proj4": "^2.7.5"
  },
  "devDependencies": {
    "parcel": "^2.0.0-beta.1"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}