globeletjs

v0.1.6

Published

3 years ago

Lightweight vector maps on a globe

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Globelet

Lightweight vector maps on a globe

Inspired by Leaflet: a simple, light-weight mapping library, without the distortion of flat maps. Show your GIS data in 3D, as it would appear from space.

See a simple interactive example with mountain peaks from Natural Earth displayed over the Mapbox Outdoors Style.

Like Leaflet, we design for simplicity, performance, and usability.

Need lots of features, like 3D buildings? Try CesiumJS. Globelet will only do a few things, but it will do them well.

How to add GlobeletJS code to your webpage

GlobeletJS is provided as an ESM import. Define your script tag as type="module", then import the module:

<script type="module">
  import * as globeletjs from "https://unpkg.com/globeletjs@<VERSION>/dist/globelet.js";

  // Add code to initialize a globe here...
  // ...
</script>

Or if you prefer, you can use the older-style IIFE bundle:

<script src="https://unpkg.com/globeletjs@<VERSION>/dist/globelet-iife.js">

Either bundle will give you a global variable globeletjs, which has an initGlobe method. See the next section for how to use this method.

Make sure to also link to the stylesheet (/dist/globelet.css) in the <head> of your HTML file.

<link 
  rel="stylesheet" 
  type="text/css" 
  href="https://unpkg.com/globeletjs@<VERSION>/dist/globelet.css">

How to initialize a globe

The globeletjs object has an initGlobe method that can initialize a new globe as follows:

const params = {
  container: 'globe',
  style: "./klokantech-basic-style-geojson.json",
  center: [-100, 38.5],
  altitude: 6280,
};

const globePromise = globeletjs.initGlobe(params);

The params object supplied to initGlobe can have the following properties:

container (REQUIRED): An HTML DIV element (or its string ID) where the globe will be displayed
infobox: An HTML DIV element (or its string ID) where information about a map feature will be displayed. NOTE: if supplied, this element will be wrapped inside a sliding pane with a close button. See the API methods showInfo and hideInfo for more information
style (REQUIRED): A link to a MapLibre style document describing the map to be rendered. Please see below for some notes about supported map styles.
mapboxToken: Your API token for Mapbox services (if needed)
width: The width of the map that will be projected onto the globe, in pixels. Defaults to container.clientWidth + 512
height: The height of the map that will be projected onto the globe, in pixels. Defaults to container.clientHeight + 512
center: The initial geographic position of the camera, given as [longitude, latitude] in degrees. Default: [0.0, 0.0]
altitude: The initial altitude of the camera, in kilometers. Default: 20000
minAltitude: The minimum altitude of the camera, in kilometers. Default: 0.0001 * earthRadius
maxAltitude: The maximum altitude of the camera, in kilometers. Default: 8.0 * earthRadius
minLongitude, minLatitude, maxLongitude, maxLatitude: Geographic limits on camera movement. By default, the globe can be spun and zoomed to any point on the planet. Setting these limits will restrict motion to a specified box. See spinning-ball documentation for further details

The returned Promise resolves to an API handle, which you can use to interact with the globe, as described in the next section.

How to interact with the globe API

The Promise returned by initGlobe resolves to an API object, which you can use to control the globe.

globePromise.then(globeAPI => {
  globeAPI.startAnimation();

  // ...etc. Do more things with globeAPI here...
});

globeAPI exposes the following properties and methods:

mapLoaded(): Returns a fractional number from 0.0 to 1.0 indicating the fraction of the tiles needed for the current view that are fully loaded
select(layer, dxy): Selects map features from the specified layer, within pixel distance dxy from the current cursor position
showLayer(layer): Turns on rendering for the specified map layer
hideLayer(layer): Turns off rendering for the specified map layer
getZoom(): Returns the current zoom level of the map
startAnimation(): Starts animation
stopAnimation(): Stops animation
update(time): Updates the camera position based on current position and velocity and cursor inputs since the last update. Input is a timestamp in milliseconds as supplied by requestAnimationFrame. For animation loops managed by the parent program
cameraPos(): Returns the camera position as reported by spinning-ball
cursorPos(): Returns the cursor position as reported by spinning-ball
isMoving(): Returns the value of the camMoving flag in spinning-ball
wasTapped(): Returns the value of the wasTapped flag in spinning-ball
addMarker(options): Adds a marker to the globe. See markers section below
removeMarker(marker): Removes a given marker from memory and from the DOM
showInfo(coords): Reveals a side pane (or bottom pane on mobile) wrapping the infobox DIV supplied on initialization, and prints the supplied coordinates (presumably [lon, lat]) in the top bar. Note: if no infobox was supplied on init, this method will do nothing
hideInfo(): Hides the infobox pane. This method will automatically be called if a user presses the close button on the pane
infoCloseButton: A link to the close button on the info pane. Can be used to execute custom scripts when the info pane is closed (e.g., to remove markers)
destroy(): Clears memory / removes elements from document

How to add and remove markers

A marker can be added to the globe as follows:

const marker = globeAPI.addMarker(options);

where options is an object with the following properties:

element: A link to an HTML Element that will be used to visualize the marker position. If not supplied, a default SVG will be used
type: The type of marker. If type === "spot", the marker element will default to a circular SVG; otherwise it defaults to a standard placemarker SVG
position: An Array containing longitude and latitude of the desired marker position, in degrees, and (optionally) the altitude in kilometers

The returned marker object has the following properties:

element: Back-link to the HTML element used to represent the marker position
position: A Float64Array containing the longitude and latitude of the marker position, in degrees, and its altitude in kilometers
screenPos: A 2-element Array containing the current screen position of the marker, in pixels from top left

At each animation frame (or each call to globeAPI.update()), GlobeletJS will automatically update screenPos, and use it to set the element's displayed position via style.left and style.top.

A marker can be removed from the globe as follows:

globeAPI.removeMarker(marker);

Supported map styles

Many features described in the style specification are not yet supported. This is partly by design--GlobeletJS is intended to be an 80/20 map solution, implementing 80% of the specification with 20% as much code as other software. But we are adding support for more features over time.

The map rendering is delegated to the tile-setter module, which is limited by some of its dependencies. See the "un-supported features" list for tile-stencil and the tile-gl TODO list for an (incomplete) list of what is not supported.

We welcome your feedback on what additional features you would like to see supported. Or better yet, try adding them yourself! See the contributing guidelines for how to get started.

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