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WebMercatorViewport

The WebMercatorViewport class takes map view states (latitude, longitude, zoom, pitch, bearing etc.), and performs projections between world and screen coordinates. It is tuned to work in synchronization with mapbox-gl's projection matrix.

Usage

The WebMercatorViewport is the default viewport for deck.gl, created under the hood by a MapView.

import {WebMercatorViewport} from '@deck.gl/core';

const viewport = new WebMercatorViewport({
  width: 600,
  height: 400,
  longitude: -122.45,
  latitude: 37.78,
  zoom: 12,
  pitch: 30,
  bearing: 15
});

viewport.project([-122.45, 37.78]);
// [300,200]

Constructor

new WebMercatorViewport({width, height, longitude, latitude, zoom, pitch, bearing});

Parameters:

  • opts (Object) - Web Mercator viewport options

    • width (Number) - Width of the viewport.
    • height (Number) - Height of the viewport.

    web mercator style arguments:

    • latitude (Number, optional) - Latitude of the viewport center on map. Default to 0.
    • longitude (Number, optional) - Longitude of the viewport center on map. Default to 0.
    • zoom (Number, optional) - Map zoom (scale is calculated as 2^zoom). Default to 11.
    • pitch (Number, optional) - The pitch (tilt) of the map from the screen, in degrees (0 is straight down). Default to 0.
    • bearing (Number, optional) - The bearing (rotation) of the map from north, in degrees counter-clockwise (0 means north is up). Default to 0.
    • altitude (Number, optional) - Altitude of camera in screen units. Default to 1.5.

    projection matrix arguments:

    • nearZMultiplier (Number, optional) - Scaler for the near plane, 1 unit equals to the height of the viewport. Default to 0.1.
    • farZMultiplier (Number, optional) - Scaler for the far plane, 1 unit equals to the distance from the camera to the top edge of the screen. Default to 1.01.
    • orthographic (Boolean, optional) - Default false.

Remarks:

  • altitude has a default value that matches assumptions in mapbox-gl
  • width and height are forced to 1 if supplied as 0, to avoid division by zero. This is intended to reduce the burden of apps to check values before instantiating a Viewport.
  • When using Mercator projection, per cartographic tradition, longitudes and latitudes are specified as degrees.
  • latitude of 90 or -90 are projected to infinity in Web Mercator projection. Using pole locations with this viewport may result in NaNs. Many base map providers cut off at 85.051129 at which the full world becomes a square.

Inherits all Viewport methods.

Methods

Inherits all methods from Viewport.

project

Projects world coordinates to pixel coordinates on screen.

Parameters:

  • coordinates (Array) - [longitude, latitude, altitude]. altitude is in meters and default to 0 if not supplied.
  • opts (Object)
    • topLeft (Boolean, optional) - Whether projected coords are top left. Default to true.

Returns:

  • [x, y] or [x, y, z] in pixels coordinates. z is pixel depth.
    • If input is [longitude, latitude]: returns [x, y].
    • If input is [longitude, latitude: altitude]: returns [x, y, z].
unproject

Unproject pixel coordinates on screen into world coordinates.

Parameters:

  • pixels (Array) - [x, y, z] in pixel coordinates. Passing a z is optional.
  • opts (Object)
    • topLeft (Boolean, optional) - Whether projected coords are top left. Default to true.
    • targetZ (Number, optional) - If pixel depth z is not specified in pixels, this is used as the elevation plane to unproject onto. Default 0.

Returns:

  • [longitude, latitude] or [longitude, latitude, altitude] in world coordinates. altitude is in meters.
    • If input is [x, y] without specifying opts.targetZ: returns [longitude, latitude].
    • If input is [x, y] with opts.targetZ: returns [longitude, latitude, targetZ].
    • If input is [x, y, z]: returns [longitude, latitude, altitude].
getDistanceScales

Returns an object with scale values supporting first order (linear) and second order (quadratic) approximations of the local Web Mercator projection scale around the viewport center. Error increases with distance from viewport center (very roughly 1% per 100km in linear mode, quadratic approximation does significantly better).

Returns:

  • An object with precalculated distance scales allowing conversion between lnglat deltas, meters and pixels.
addMetersToLngLat

Add a meter delta to a base lnglat coordinate using linear approximation. For information on numerical precision, see remarks on getDistanceScales.

Parameters:

  • lngLatZ (Array) - Base coordinate in [longitude, latitude, altitude]. Passing a altitude is optional.
  • xyz (Array) - Array of [x, y, z] in meter deltas. Passing a z is optional.

Returns:

  • New coordinate array in [longitude, latitude] or [longitude, latitude, altitude] if z is provided.
fitBounds

Returns a new viewport that fit around the given bounding box. Only supports non-perspective mode.

Parameters:

  • bounds (Array) - Bounding box in [[longitude, latitude], [longitude, latitude]].
  • opts (Object)
    • padding (Number) - The amount of padding in pixels to add to the given bounds.
    • offset (Array) - The center in [x, y] of the given bounds relative to the map's center measured in pixels.

Returns:

  • New WebMercatorViewport fit around the gven bounding box.

Remarks

  • Because WebMercatorViewport a subclass of Viewport, an application can implement support for generic 3D Viewports and automatically get the ability to accept web mercator style map coordinates.
  • A limitation at the moment is that there is no way to extract web mercator parameters from a "generic" viewport, so for map synchronization applications (rendering on top of a typical map component that only accepts web mercator parameters) the WebMercatorViewport is necessary.
  • Facilitates the necessary mercator projections by breaking them into a minimal non-linear piece followed by a standard projection chain.
  • Making deck.gl work with non-mapbox map systems in perspective mode might require subclassing WebMercatorViewport and adjust the projection so it matches the map's projection.

Source

modules/core/src/viewports/web-mercator-viewport.js