@allmaps/maplibre

Allmaps plugin for MapLibre GL. This plugin allows displaying georeferenced IIIF images on a MapLibre map. The plugin works by loading Georeference Annotations and uses WebGL to transform images from a IIIF image server to overlay them on their correct geographical position.

See allmaps.org for more information.

Examples:

• Observable notebook
• Observable notebook

How it works

This plugin creates a new class WarpedMapLayer which extends MapLibre’s CustomLayerInterface. You can add one or multiple Georeference Annotations (or AnnotationPages with multiple Georeference Annotations) to a WarpedMapLayer, and add the WarpedMapLayer to your MapLibre map. This will render all georeferenced maps contained in the Georeference Annotation on your MapLibre map.

To understand what happens under the hood for each georeferenced map, see the @allmaps/render package.

This plugin inherits a lot of methods from @allmaps/warpedmaplayer, the core package gathering the functionality connecting the Allmaps plugins to the @allmaps/render package.

Installation

This package works in browsers and in Node.js as an ESM or an UMD module.

Install with pnpm:

pnpm install @allmaps/maplibre

You can optionally build this package locally by running:

pnpm run build

The easiest way to test this package during local development is via @allmaps/test-plugins. A minimal example is also included in ./index.html and can be served via pnpm run dev.

Usage

Built for MapLibre 5.0, but should work with earlier versions as well.

Adding a WarpedMapLayer to a MapLibre Map

Creating a WarpedMapLayer and adding it to a map looks like this:

import { Map as MapLibreMap } from 'maplibre-gl'
import { WarpedMapLayer } from '@allmaps/maplibre'

const map = new MapLibreMap({
  container: 'map',
  // @ts-expect-error MapLibre types are incompatible
  style: 'https://basemaps.cartocdn.com/gl/voyager-gl-style/style.json',
  center: [-73.9337, 40.8011],
  zoom: 11.5,
  // Pitch is currently not supported by the Allmaps plugin for MapLibre
  maxPitch: 0
})

const annotationUrl = 'https://annotations.allmaps.org/images/d180902cb93d5bf2'
const warpedMapLayer = new WarpedMapLayer()

map.on('load', () => {
  // @ts-expect-error MapLibre types are incompatible
  map.addLayer(warpedMapLayer)
  warpedMapLayer.addGeoreferenceAnnotationByUrl(annotationUrl)
})

WarpedMapLayer is implemented using MapLibre’s CustomLayerInterface. It can be added to a map like any other MapLibre layer, but there are some things to take into account:

• WarpedMapLayer does not make use of a Source (although that could be implemented in the future, similar to @allmaps/openlayers).
• WarpedMapLayer currently does not support pitch, so disable it on your map.
• Just like other MapLibre layers, a WarpedMapLayer must have a unique id. By default, the id has the value warped-map-layer. When adding multiple WarpedMapLayers to your map, pass a unique id to their constructor:

const warpedMapLayerWithUniqueId = new WarpedMapLayer({layerId: 'my-unique-id'})

Ways to load Georeference Annotations

Once the layer has been added to the map, a Georeference Annotation can be added to a WarpedMapLayer using the addGeoreferenceAnnotation and addGeoreferenceAnnotationByUrl functions:

fetch(annotationUrl)
  .then((response) => response.json())
  .then((annotation) => warpedMapLayer.addGeoreferenceAnnotation(annotation))

Or:

await warpedMapLayer.addGeoreferenceAnnotationByUrl(annotationUrl)

It’s also possible to create a WarpedMapList first and pass it to the layer on creation. This has the advantage of being able to compute properties of a WarpedMapList first, e.g. getting the bounds and passing it to the MapLibre Map.

import { Map as MapLibreMap } from 'maplibre-gl'

import { WarpedMapLayer } from '@allmaps/maplibre'
import { WarpedMapList } from '@allmaps/render'
import { WebGL2WarpedMap } from '@allmaps/render/webgl2'

const annotationUrl = 'https://annotations.allmaps.org/images/d180902cb93d5bf2'
const annotation = await fetch(annotationUrl).then((response) =>
    response.json()
  )

const warpedMapList = new WarpedMapList<WebGL2WarpedMap>()
await warpedMapList.addGeoreferenceAnnotation(annotation)
const bbox = warpedMapList.getMapsBbox()

map = new MapLibreMap({
  container: 'map',
  // @ts-expect-error MapLibre types are incompatible
  style: 'https://basemaps.cartocdn.com/gl/voyager-gl-style/style.json',
  // Pitch is currently not supported by the Allmaps plugin for MapLibre
  maxPitch: 0
})

map.on('load', () => {
  const warpedMapLayer = new WarpedMapLayer({ warpedMapList })
  // @ts-expect-error MapLibre types are incompatible
  map.addLayer(warpedMapLayer)
  if (bbox) {
    map.fitBounds(bbox, { padding: 20 })
  }
})

Note that the ...ByUrl() functions are not available on a WarpedMapList.

WarpedMapLayer API, Options and Events

See the @allmaps/warpedmaplayer package for the API documentation of the methods coming from the WarpedMapLayer class (shared by all Allmaps plugins). It describes the methods like addGeoreferenceAnnotation() and includes a list of all options that can be set on instances of the class and all events which are passed to the native map instance hosting the layer instance.

You can set options on the entire layer, or on a specific map on the layer (overwriting layer options):

warpedMapLayer.setLayerOptions({ visible: true })
warpedMapLayer.setMapOptions(mapId, { visible: true })

You can listen to events in the typical way:

map.on('warpedmapadded', (event) => {
  console.log(event.mapIds)
})

License

MIT

API

MapLibreWarpedMapLayerOptions

Type

SpecificMapLibreWarpedMapLayerOptions & Partial<WebGL2RenderOptions>

new WarpedMapLayer(options)

Creates a WarpedMapLayer instance

Parameters

• options? (Partial<MapLibreWarpedMapLayerOptions> | undefined)
  • options

Returns

WarpedMapLayer.

Extends

• BaseWarpedMapLayer
• CustomLayerInterface

WarpedMapLayer#getBounds()

Get the bounding box of all maps as a MapLibre LngLatBoundsLike object

This is the default MapLibre getBounds() function

The result is returned in lon-lat EPSG:4326.

Parameters

There are no parameters.

Returns

bounding box of all maps (LngLatBoundsLike | undefined).

WarpedMapLayer#getCenterZoomBearing(options)

Get the center, zoom and bearing needed to make the Maplibre Map’s viewport fit all maps in the layer.

This can be used as input for

• Map.jumpTo() for immediate change
• Map.easeTo() for smooth panning
• Map.flyTo() for a flying animation which zooms out and in

Parameters

• options? ( | Partial< CenterZoomBearingOptions & CenterZoomBearing & { pitch?: number roll?: number elevation?: number } & { padding?: number | PaddingOptions offset?: PointLike maxZoom?: number } > | undefined)

Returns

center, zoom and bearing ({center?: LngLatLike; zoom?: number; bearing?: number}).

WarpedMapLayer#getMapsBounds(mapIds)

Get the bounding box of all selected maps as a MapLibre LngLatBoundsLike object

This is the default MapLibre getBounds() function

The result is returned in lon-lat EPSG:4326.

Parameters

• mapIds (Array<string>)
  • Map IDs

Returns

bounding box of all selected maps (LngLatBoundsLike | undefined).

WarpedMapLayer#getMapsCenterZoomBearing(mapIds, options)

Get the center, zoom and bearing needed to make the Maplibre Map’s viewport fit all selected maps.

This can be used as input for

• Map.jumpTo() for immediate change
• Map.easeTo() for smooth panning
• Map.flyTo() for a flying animation which zooms out and back in

Parameters

• mapIds (Array<string>)
• options? ( | Partial< CenterZoomBearingOptions & CenterZoomBearing & { pitch?: number roll?: number elevation?: number } & { padding?: number | PaddingOptions offset?: PointLike maxZoom?: number } > | undefined)

Returns

center, zoom and bearing ({center?: LngLatLike; zoom?: number; bearing?: number}).

WarpedMapLayer#id

Type

string

WarpedMapLayer#map?

Type

MaplibreMap

WarpedMapLayer#nativePassWarpedMapEvent(event)

Pass events

Parameters

• event (Event)

Returns

void.

WarpedMapLayer#nativeUpdate()

Trigger the native update function of the map

Parameters

There are no parameters.

Returns

void.

WarpedMapLayer#onAdd(map, gl)

Method called when the layer has been added to the Map.

Parameters

• map (MaplibreMap)
  • The Map this custom layer was just added to.
• gl (WebGL2RenderingContext)
  • The WebGL 2 context for the map.

Returns

void.

WarpedMapLayer#onRemove()

Method called when the layer has been removed from the Map.

Parameters

There are no parameters.

Returns

void.

WarpedMapLayer#render()

Render the layer.

Parameters

There are no parameters.

Returns

void.

WarpedMapLayer#renderingMode

Type

'2d'

WarpedMapLayer#type

Type

'custom'