Timezones in KML

Demonstrates rendering timezones from KML.

This example parses a KML file and renders the features as a vector layer. The layer is given a ol/style/Style that fills timezones yellow with an opacity calculated based on the current offset to local noon.

main.js

import 'ol/ol.css';
import KML from 'ol/format/KML';
import Map from 'ol/Map';
import Stamen from 'ol/source/Stamen';
import VectorSource from 'ol/source/Vector';
import View from 'ol/View';
import {Fill, Stroke, Style} from 'ol/style';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';

/*
 * Compute the style of the feature.  Here we want the opacity of polygons to
 * be based on the offset from local noon.  For example, a timezone where it is
 * currently noon would have an opacity of 0.75.  And a timezone where it is
 * currently midnight would have an opacity of 0.  This doesn't account for
 * daylight savings, so don't use it to plan your vacation.
 */
const styleFunction = function (feature) {
  let offset = 0;
  const name = feature.get('name'); // e.g. GMT -08:30
  const match = name.match(/([\-+]\d{2}):(\d{2})$/);
  if (match) {
    const hours = parseInt(match[1], 10);
    const minutes = parseInt(match[2], 10);
    offset = 60 * hours + minutes;
  }
  const date = new Date();
  const local = new Date(
    date.getTime() + (date.getTimezoneOffset() + offset) * 60000
  );
  // offset from local noon (in hours)
  let delta = Math.abs(12 - local.getHours() + local.getMinutes() / 60);
  if (delta > 12) {
    delta = 24 - delta;
  }
  const opacity = 0.75 * (1 - delta / 12);
  return new Style({
    fill: new Fill({
      color: [0xff, 0xff, 0x33, opacity],
    }),
    stroke: new Stroke({
      color: '#ffffff',
    }),
  });
};

const vector = new VectorLayer({
  source: new VectorSource({
    url: 'data/kml/timezones.kml',
    format: new KML({
      extractStyles: false,
    }),
  }),
  style: styleFunction,
});

const raster = new TileLayer({
  source: new Stamen({
    layer: 'toner',
  }),
});

const map = new Map({
  layers: [raster, vector],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

const info = $('#info');
info.tooltip({
  animation: false,
  trigger: 'manual',
});

const displayFeatureInfo = function (pixel) {
  info.css({
    left: pixel[0] + 'px',
    top: pixel[1] - 15 + 'px',
  });
  const feature = map.forEachFeatureAtPixel(pixel, function (feature) {
    return feature;
  });
  if (feature) {
    info.attr('data-original-title', feature.get('name')).tooltip('show');
  } else {
    info.tooltip('hide');
  }
};

map.on('pointermove', function (evt) {
  if (evt.dragging) {
    info.tooltip('hide');
    return;
  }
  displayFeatureInfo(map.getEventPixel(evt.originalEvent));
});

map.on('click', function (evt) {
  displayFeatureInfo(evt.pixel);
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Timezones in KML</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>
    <script src="https://code.jquery.com/jquery-3.5.1.min.js"></script>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css">
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.0/js/bootstrap.bundle.min.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
      #map {
        position: relative;
      }
      #info {
        position: absolute;
        height: 1px;
        width: 1px;
        z-index: 100;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"><div id="info"></div></div>
    <script src="main.js"></script>
  </body>
</html>

package.json

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