Tissot Indicatrix

EPSG:4326

EPSG:3857

Draw Tissot's indicatrices on maps.

Example of Tissot indicatrix maps. The map on the top is an EPSG:4326 map. The one on the bottom is EPSG:3857.

main.js

import 'ol/ol.css';
import Feature from 'ol/Feature';
import Map from 'ol/Map';
import TileWMS from 'ol/source/TileWMS';
import VectorSource from 'ol/source/Vector';
import View from 'ol/View';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {circular as circularPolygon} from 'ol/geom/Polygon';

const vectorLayer4326 = new VectorLayer({
  source: new VectorSource(),
});

const vectorLayer3857 = new VectorLayer({
  source: new VectorSource(),
});

const map4326 = new Map({
  layers: [
    new TileLayer({
      source: new TileWMS({
        url: 'https://ahocevar.com/geoserver/wms',
        params: {
          'LAYERS': 'ne:NE1_HR_LC_SR_W_DR',
          'TILED': true,
        },
      }),
    }),
    vectorLayer4326,
  ],
  target: 'map4326',
  view: new View({
    projection: 'EPSG:4326',
    center: [0, 0],
    zoom: 2,
  }),
});

const map3857 = new Map({
  layers: [
    new TileLayer({
      source: new TileWMS({
        url: 'https://ahocevar.com/geoserver/wms',
        params: {
          'LAYERS': 'ne:NE1_HR_LC_SR_W_DR',
          'TILED': true,
        },
      }),
    }),
    vectorLayer3857,
  ],
  target: 'map3857',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

const radius = 800000;
let x, y;
for (x = -180; x < 180; x += 30) {
  for (y = -90; y <= 90; y += 30) {
    const circle4326 = circularPolygon([x, y], radius, 64);
    const circle3857 = circle4326.clone().transform('EPSG:4326', 'EPSG:3857');
    vectorLayer4326.getSource().addFeature(new Feature(circle4326));
    vectorLayer3857.getSource().addFeature(new Feature(circle3857));
  }
}

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Tissot Indicatrix</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <!-- The lines below are 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,TextDecoder"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <h4>EPSG:4326</h4>
    <div id="map4326" class="map"></div>
    <h4>EPSG:3857</h4>
    <div id="map3857" class="map"></div>
    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "tissot",
  "dependencies": {
    "ol": "6.13.1-dev"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}