Image Map Types

by Abdrey Katrusha

HTML

<!DOCTYPE html>
<html>
  <head>
    <title>Image Map Types</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>
    <!-- jsFiddle will insert css and js -->
  </head>
  <body>
    <div id="map"></div>

    <!-- Async script executes immediately and must be after any DOM elements used in callback. -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=AIzaSyBIwzALxUPNbatRBj3Xi1Uhp0fFzwWNBkE&callback=initMap&libraries=&v=weekly"
      async
    ></script>
  </body>
</html>

CSS

/* Always set the map height explicitly to define the size of the div
       * element that contains the map. */
#map {
  height: 100%;
}

/* Optional: Makes the sample page fill the window. */
html,
body {
  height: 100%;
  margin: 0;
  padding: 0;
}

JavaScript

function initMap() {
  const map = new google.maps.Map(document.getElementById("map"), {
    center: { lat: 0, lng: 0 },
    zoom: 1,
    streetViewControl: false,
    mapTypeControlOptions: {
      mapTypeIds: ["moon"],
    },
  });
  const moonMapType = new google.maps.ImageMapType({
    getTileUrl: function (coord, zoom) {
      const normalizedCoord = getNormalizedCoord(coord, zoom);

      if (!normalizedCoord) {
        return "";
      }
      const bound = Math.pow(2, zoom);
      return (
        "https://mw1.google.com/mw-planetary/lunar/lunarmaps_v1/clem_bw" +
        "/" +
        zoom +
        "/" +
        normalizedCoord.x +
        "/" +
        (bound - normalizedCoord.y - 1) +
        ".jpg"
      );
    },
    tileSize: new google.maps.Size(256, 256),
    maxZoom: 9,
    minZoom: 0,
    radius: 1738000,
    name: "Moon",
  });
  map.mapTypes.set("moon", moonMapType);
  map.setMapTypeId("moon");
}

// Normalizes the coords that tiles repeat across the x axis (horizontally)
// like the standard Google map tiles.
function getNormalizedCoord(coord, zoom) {
  const y = coord.y;
  let x = coord.x;
  // tile range in one direction range is dependent on zoom level
  // 0 = 1 tile, 1 = 2 tiles, 2 = 4 tiles, 3 = 8 tiles, etc
  const tileRange = 1 << zoom;

  // don't repeat across y-axis (vertically)
  if (y < 0 || y >= tileRange) {
    return null;
  }

  // repeat across x-axis
  if (x < 0 || x >= tileRange) {
    x = ((x % tileRange) + tileRange) % tileRange;
  }
  return { x: x, y: y };
}