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

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>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <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 type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "tissot",
  "dependencies": {
    "ol": "9.1.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}