proj4leaflet

Smooth Proj4js integration with Leaflet

npm install proj4leaflet
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Proj4Leaflet NPM version

This Leaflet plugin adds support for using projections supported by Proj4js.

Leaflet comes with built in support for tiles in Spherical Mercator. If you need support for tile layers in other projections, the Proj4Leaflet plugin lets you use tiles in any projection supported by Proj4js, which means support for just about any projection commonly used.

Proj4Leaflet also adds support for GeoJSON in any projection, while Leaflet by itself assumes GeoJSON to always use WGS84 as its projection.

For more details, see this blog post on tiling and projections.

Usage

Common use means making a new CRS instance for the projection you want to use.

// RT90 with map's pixel origin at RT90 coordinate (0, 0)
var crs = new L.Proj.CRS('EPSG:2400',
  '+lon_0=15.808277777799999 +lat_0=0.0 +k=1.0 +x_0=1500000.0 ' +
  '+y_0=0.0 +proj=tmerc +ellps=bessel +units=m ' +
  '+towgs84=414.1,41.3,603.1,-0.855,2.141,-7.023,0 +no_defs',
  {
    resolutions: [8192, 4096, 2048], // 3 example zoom level resolutions
  }
);

var map = L.map('map', {
  crs: crs,
  continuousWorld: true,
  worldCopyJump: false
});
L.tileLayer('http://tile.example.com/example/{z}/{x}/{y}.png').addTo(map);

Using options when constructing the CRS, you can set the tile set's origin:

// SWEREF 99 TM with map's pixel origin at (218128.7031, 6126002.9379)
var crs = new L.Proj.CRS('EPSG:3006',
  '+proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs',
  {
    origin: [218128.7031, 6126002.9379],
    resolutions: [8192, 4096, 2048], // 3 example zoom level resolutions
  }
);

To use a TMS tile server, you must use a the class L.Proj.CRS.TMS as your CRS. Also, the tms option must be set on the L.TileLayer instance.

// EPSG:102012 served by TMS with bounds (-5401501.0, 4065283.0, 4402101.0, 39905283.0)
new L.Proj.CRS.TMS('EPSG:102012',
    '+proj=lcc +lat_1=30 +lat_2=62 +lat_0=0 +lon_0=105 +x_0=0 +y_0=0 '
    + '+ellps=WGS84 +datum=WGS84 +units=m +no_defs',
    [-5401501.0, 4065283.0, 4402101.0, 39905283.0],
    {
        resolutions: [
           140000.0000000000,
            70000.0000000000,
            35000.0000000000,
            17500.0000000000
        ]
    }
);

...

L.tileLayer('http://tile.example.com/example/{z}/{x}/{y}.png', {tms: true}).addTo(map);

(See reference for L.CRS.TMS for details on TMS and Leaflet versions before 0.7.)

Proj4js compatibility notice

Proj4js has breaking changes introduced after version 1.1.0. The current version of Proj4Leaflet uses Proj4js 1.3.4 or later. If you for some reason need Proj4js version 1.1.0 compatibility, you can still use Proj4Leaflet version 0.5.

API

The plugin extends Leaflet with a few classes that helps integrating Proj4's projections into Leaflet's ICRS interface.

L.Proj.CRS

An ICRS implementation that uses a Proj4 definition for the projection. This is likely to be the only class you need to work with in Proj4Leaflet.

Usage example

var map = L.map('map', {
    center: [57.74, 11.94],
    zoom: 13,
    crs: L.Proj.CRS('EPSG:2400',
      '+lon_0=15.808277777799999 +lat_0=0.0 +k=1.0 +x_0=1500000.0 ' +
      '+y_0=0.0 +proj=tmerc +ellps=bessel +units=m ' +
      '+towgs84=414.1,41.3,603.1,-0.855,2.141,-7.023,0 +no_defs',
      {
        resolutions: [8192, 4096, 2048], // 3 example zoom level resolutions
      });
    continuousWorld: true,
    worldCopyJump: false
});

Constructor

L.Proj.CRS(code, proj4def, options)
  • code is the projection's SRS code (only used internally by the Proj4js library).
  • proj4def is the Proj4 definition for the projection to use
  • options is an options object with these possible options:
    • origin: the projected coordinate to use as the map's pixel origin; overrides the transformation option if set
    • transformation: an L.Transformation that is used to transform the projected coordinates to pixel coordinates; default is L.Transformation(1, 0, -1, 0)
    • scales: an array of scales (pixels per projected coordinate unit) for each corresponding zoom level; default is to use Leaflet's native scales. You should use scales or resolutions, not both.
    • resolutions: an array of resolutions (projected coordinate units per pixel) for each corresponding zoom level; default is to use Leaflet's native resolutions. You should use scales or resolutions, not both.

L.Proj.CRS.TMS

ICRS implementation to work with a Proj4 projection that will be used together with a TMS tile server. Since TMS has its y axis in the opposite direction of Leaflet (and OpenStreetMap/Google Maps), this requires some extra work.

Note: If you use TMS and Leaflet before version 0.7, you must use L.Proj.TileLayerTMS instead of a standard L.TileLayer; the standard TileLayer before 0.7 couldn't handle other projections than spherical Mercator together with TMS.

Usage example

var map = new L.Map('map', {
    crs: new L.Proj.CRS.TMS('EPSG:102012',
        '+proj=lcc +lat_1=30 +lat_2=62 +lat_0=0 +lon_0=105 +x_0=0 +y_0=0 '
        + '+ellps=WGS84 +datum=WGS84 +units=m +no_defs',
        [-5401501.0, 4065283.0, 4402101.0, 39905283.0],
        {
            resolutions: [
               140000.0000000000,
                70000.0000000000,
                35000.0000000000,
                17500.0000000000
            ]
        }
    ),
    continuousWorld: true,
    worldCopyJump: false
});

Constructor

L.Proj.CRS.TMS(code, proj4def, projectedBounds, options)
  • code is the projection's SRS code (only used internally by the Proj4js library).
  • proj4def is the Proj4 definition for the projection to use
  • projectedBounds the bounds of the TMS tile grid in projected coordinates. The bounds need to be properly specified and align to the grid on all provided zoom levels, or markers and/or tiles will not align properly with the corresponding WGS84 coordinate.
  • options is an options object with the same keys as L.Proj.CRS. It also accepts one extra option:
    • tileSize: sets the tile size (in pixels) which the CRS should align to; in case the projected bounds do not align with the tile grid, CRS will align it using this tile size. Default is 256.

L.Proj.TileLayer.TMS

Deprecated since version 0.7, since Leaflet 0.7 does not need this class.

Extends L.TileLayer to support TMS when working with Proj4 projections. Note that for Leaflet versions before 0.7, L.TileLayer will not work with other projections than EPSG:3857 if the option tms is enabled.

Usage example

var crs = new L.Proj.CRS.TMS(...),
    map = new L.Map('map', {
        crs: crs,
        continuousWorld: true,
        worldCopyJump: false
    }),

map.addLayer(new L.Proj.TileLayer.TMS('http://{s}.my-tms-server/{z}/{x}/{y}.png', crs, {
    maxZoom: 17
    ,minZoom: 0
    ,continuousWorld: true
    ,attribution: attrib
}));

Constructor

L.Proj.TileLayer.TMS(tileUrl, crs, options)
  • tileUrl is the URL template to use for tiles (see L.TileLayer)
  • crs is the L.Proj.CRS.TMS ICRS object used for this layer
  • options are the options for this layer, see L.TileLayer

L.Proj.GeoJSON

Extends L.GeoJSON to add CRS support. Unlike the TileLayer extension, the CRS is derived from the name property of a crs defined directly on the GeoJSON object per the spec. Linked CRSs are not supported.

Note: The relevant Proj4 definition should be defined directly via proj4.defs before loading the GeoJSON object. If it is not, proj4leaflet will throw an error.

Also, note that future versions of the GeoJSON spec may not include explicit CRS support. See https://github.com/GeoJSONWG/draft-geojson/pull/6 for more information.

Usage Example

proj4.defs("urn:ogc:def:crs:EPSG::26915", "+proj=utm +zone=15 +ellps=GRS80 +datum=NAD83 +units=m +no_defs");
var geojson = {
  "type": "Feature",
  "geometry": {
    "type": "Point",
    "coordinates": [481650, 4980105]
  },
  "crs": {
    "type": "name",
    "properties": {
      "name": "urn:ogc:def:crs:EPSG::26915"
    }
  }
};
var map = L.map('map');
// ...
L.Proj.geoJson(geojson).addTo(map);
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