Web Development

view: new ol.View({ center: [14682762,5326473], zoom: 7, minZoom:3, maxZoom:19 })

view: new ol.View({ center: ol.proj.fromLonLat([137, 43]), zoom: 4, minZoom:2, maxZoom:23 })

view: new ol.View({ center: ol.proj.transform( [-122.416667, 37.783333], 'EPSG:4326', 'EPSG:3857'), zoom: 12 })

The ol.proj namespace stores:

    a list of ol.proj.Projection objects, one for each projection supported by the application
    a list of transform functions needed to convert coordinates in one projection into another.

The static functions are the methods used to maintain these. Each transform function can handle not only simple coordinate pairs, but also large arrays of coordinates such as vector geometries.

When loaded, the library adds projection objects for EPSG:4326 (WGS84 geographic coordinates) and EPSG:3857 (Web or Spherical Mercator, as used for example by Bing Maps or OpenStreetMap), together with the relevant transform functions.

Additional transforms may be added by using the http://proj4js.org/ library (version 2.2 or later). You can use the full build supplied by Proj4js, or create a custom build to support those projections you need; see the Proj4js website for how to do this. You also need the Proj4js definitions for the required projections. These definitions can be obtained from https://epsg.io/, and are a JS function, so can be loaded in a script tag (as in the examples) or pasted into your application. The first time there is a request for a projection, either with a ol.proj.projectionLike or directly with ol.proj.get, the code will check if the Proj4js library and the necessary definition are loaded; if so, it will register the appropriate ol.proj.Projection object and add transform functions between the new projection and all the existing ones. See examples/wms-image-custom-proj for an example of this. Because the check for presence of the Proj4js library and the definition only takes place on the first request for them, this means they can be loaded dynamically as needed; for example, with user-supplied data where you don't know in advance what projections are needed, you can initially load minimal support and then load whichever are requested.

Note that Proj4js does not support projection extents. If you want to add one for creating default tile grids, you can add it after the Projection object has been created with setExtent, for example, ol.proj.get('EPSG:1234').setExtent(extent).

In addition to Proj4js support, any transform functions can be added with ol.proj.addCoordinateTransforms. To use this, you must first create a ol.proj.Projection object for the new projection and add it with ol.proj.addProjection. You can then add the forward and inverse functions with ol.proj.addCoordinateTransforms. See examples/wms-custom-proj for an example of this.

Note that if no transforms are needed and you only need to define the projection, just add a ol.proj.Projection with ol.proj.addProjection. See examples/wms-no-proj for an example of this.

Classes

Projection

Members

ol.proj.METERS_PER_UNIT{Object.<ol.proj.Units, number>}

    Meters per unit lookup table.

Methods

ol.proj.addCoordinateTransforms(source, destination, forward, inverse)
src/ol/proj.js, line 218

    Registers coordinate transform functions to convert coordinates between the source projection and the destination projection. The forward and inverse functions convert coordinate pairs; this function converts these into the functions used internally which also handle extents and coordinate arrays.
    Name  Type  Description
    source  ol.ProjectionLike 

    Source projection.
    destination  ol.ProjectionLike 

    Destination projection.
    forward  function 

    The forward transform function (that is, from the source projection to the destination projection) that takes a ol.Coordinate as argument and returns the transformed ol.Coordinate.
    inverse  function 

    The inverse transform function (that is, from the destination projection to the source projection) that takes a ol.Coordinate as argument and returns the transformed ol.Coordinate.

ol.proj.addEquivalentProjections(projections)
src/ol/proj.js, line 118

    Registers transformation functions that don't alter coordinates. Those allow to transform between projections with equal meaning.
    Name  Type  Description
    projections  Array.<ol.proj.Projection> 

    Projections.

ol.proj.addProjection(projection)
src/ol/proj.js, line 160

    Add a Projection object to the list of supported projections that can be looked up by their code.
    Name  Type  Description
    projection  ol.proj.Projection 

    Projection instance.

ol.proj.equivalent(projection1, projection2){boolean}
src/ol/proj.js, line 335

    Checks if two projections are the same, that is every coordinate in one projection does represent the same geographic point as the same coordinate in the other projection.
    Name  Type  Description
    projection1  ol.proj.Projection 

    Projection 1.
    projection2  ol.proj.Projection 

    Projection 2.

    Returns:
    Equivalent.
ol.proj.fromLonLat(coordinate, opt_projection){ol.Coordinate}
src/ol/proj.js, line 270

    Transforms a coordinate from longitude/latitude to a different projection.
    Name  Type  Description
    coordinate  ol.Coordinate 

    Coordinate as longitude and latitude, i.e. an array with longitude as 1st and latitude as 2nd element.
    projection  ol.ProjectionLike 

    Target projection. The default is Web Mercator, i.e. 'EPSG:3857'.

    Returns:
    Coordinate projected to the target projection.
ol.proj.get(projectionLike){ol.proj.Projection}
src/ol/proj.js, line 305

    Fetches a Projection object for the code specified.
    Name  Type  Description
    projectionLike  ol.ProjectionLike 

    Either a code string which is a combination of authority and identifier such as "EPSG:4326", or an existing projection object, or undefined.

    Returns:
    Projection object, or null if not in list.
ol.proj.getPointResolution(projection, resolution, point, opt_units){number}
src/ol/proj.js, line 72

    Get the resolution of the point in degrees or distance units. For projections with degrees as the unit this will simply return the provided resolution. For other projections the point resolution is by default estimated by transforming the 'point' pixel to EPSG:4326, measuring its width and height on the normal sphere, and taking the average of the width and height. A custom function can be provided for a specific projection, either by setting the getPointResolution option in the ol.proj.Projection constructor or by using ol.proj.Projection#setGetPointResolution to change an existing projection object.
    Name  Type  Description
    projection  ol.ProjectionLike 

    The projection.
    resolution  number 

    Nominal resolution in projection units.
    point  ol.Coordinate 

    Point to find adjusted resolution at.
    units  ol.proj.Units 

    Units to get the point resolution in. Default is the projection's units.

    Returns:
    Point resolution.
ol.proj.getTransform(source, destination){ol.TransformFunction}
src/ol/proj.js, line 360

    Given the projection-like objects, searches for a transformation function to convert a coordinates array from the source projection to the destination projection.
    Name  Type  Description
    source  ol.ProjectionLike 

    Source.
    destination  ol.ProjectionLike 

    Destination.

    Returns:
    Transform function.
ol.proj.setProj4(proj4)
src/ol/proj.js, line 46

    Register proj4. If not explicitly registered, it will be assumed that proj4js will be loaded in the global namespace. For example in a browserify ES6 environment you could use:

    import ol from 'openlayers';
    import proj4 from 'proj4';
    ol.proj.setProj4(proj4);

    Name  Type  Description
    proj4  Proj4 

    Proj4.

ol.proj.toLonLat(coordinate, opt_projection){ol.Coordinate}
src/ol/proj.js, line 285

    Transforms a coordinate to longitude/latitude.
    Name  Type  Description
    coordinate  ol.Coordinate 

    Projected coordinate.
    projection  ol.ProjectionLike 

    Projection of the coordinate. The default is Web Mercator, i.e. 'EPSG:3857'.

    Returns:
    Coordinate as longitude and latitude, i.e. an array with longitude as 1st and latitude as 2nd element.
ol.proj.transform(coordinate, source, destination){ol.Coordinate}
src/ol/proj.js, line 458

    Transforms a coordinate from source projection to destination projection. This returns a new coordinate (and does not modify the original).

    See ol.proj.transformExtent for extent transformation. See the transform method of ol.geom.Geometry and its subclasses for geometry transforms.
    Name  Type  Description
    coordinate  ol.Coordinate 

    Coordinate.
    source  ol.ProjectionLike 

    Source projection-like.
    destination  ol.ProjectionLike 

    Destination projection-like.

    Returns:
    Coordinate.
ol.proj.transformExtent(extent, source, destination){ol.Extent}
src/ol/proj.js, line 474

    Transforms an extent from source projection to destination projection. This returns a new extent (and does not modify the original).
    Name  Type  Description
    extent  ol.Extent 

    The extent to transform.
    source  ol.ProjectionLike 

    Source projection-like.
    destination  ol.ProjectionLike 

    Destination projection-like.

    Returns:
    The transformed extent.