projections

This module wraps proj4 to manage coordinate reference system (CRS) definitions.

The WGS84 constant ('WGS84') is the canonical name used by the library for the WGS84 geographic coordinate reference system.

In addition to the projections provided by proj4, several common projections and WGS84 aliases are automatically registered when the module is loaded.

The following projections are available by default:

Name	Description
WGS84	WGS84 geographic CRS
EPSG:4326	WGS84 geographic CRS
CRS:84	OGC WGS84 geographic CRS
CRS84	Alias for CRS:84
EPSG:3857	Web Mercator
EPSG:2154	RGF93 / Lambert-93

Common OGC URN aliases for WGS84 are also supported.

Additional projections can be registered using defineProjection().

normalizeCrsName

Signature

normalizeCrsName(name)

Description

Normalizes an OGC EPSG URN to its short EPSG:<code> form.

Other CRS names are returned unchanged.

Parameters

Name	Type	Required	Description
name	string	yes	CRS name to normalize

Returns

Type	Description
string	The normalized CRS name

Throws

Throws if name is not a non-empty string.

Examples

normalizeCrsName('urn:ogc:def:crs:EPSG::2154')
// 'EPSG:2154'

normalizeCrsName('EPSG:2154')
// 'EPSG:2154'

normalizeCrsName('CRS:84')
// 'CRS:84'

listProjections

Signature

listProjections()

Description

Returns the names of all registered projections.

This includes projections provided by proj4, projections registered by common-geospatial, and projections added through defineProjection().

Returns

Type	Description
string[]	Array of registered projection names

Examples

listProjections()
// ['EPSG:4326', 'EPSG:3857', 'WGS84', 'CRS:84', 'EPSG:2154', ...]

defineProjection

Signature

defineProjection(name, definition)

Description

Defines a projection under the given name.

The definition may be either a Proj4 definition string or a Proj4 definition object. If a projection with the same name already exists, it is replaced.

Parameters

Name	Type	Required	Description
name	string	yes	Projection name, for example EPSG:2154
definition	string | object	yes	Proj4 definition string or definition object

Throws

Throws if name is not a non-empty string or if definition is neither a non-empty string nor a non-empty object.

Examples

defineProjection(
  'EPSG:32631',
  '+proj=utm +zone=31 +datum=WGS84 +units=m +no_defs'
)

hasProjection

Signature

hasProjection(name)

Description

Returns whether a projection with the given name is defined.

Parameters

Name	Type	Required	Description
name	string	yes	Projection name

Returns

Type	Description
boolean	true if the projection exists

Throws

Throws if name is not a non-empty string.

Examples

hasProjection('EPSG:2154')
// true

hasProjection('UNKNOWN')
// false

getProjection

Signature

getProjection(name)

Description

Returns the Proj4 definition associated with the given projection name.

Parameters

Name	Type	Required	Description
name	string	yes	Projection name

Returns

Type	Description
object | undefined	Projection definition, or undefined if the projection is not defined

Throws

Throws if name is not a non-empty string.

Examples

getProjection('EPSG:2154')
// { projName: 'lcc', ... }

getProjection('UNKNOWN')
// undefined

isWGS84Projection

Signature

isWGS84Projection(name)

Description

Returns whether the registered projection is recognized as a WGS84 geographic projection based on its projection and datum definitions.

INFO

The comparison is performed against the registered EPSG:4326 definition.

Parameters

Name	Type	Required	Description
name	string	yes	Projection name

Returns

Type	Description
boolean	true if the projection is equivalent to WGS84

Throws

Throws if name is not a non-empty string.

Examples

isWGS84Projection('EPSG:4326')
// true

isWGS84Projection('CRS:84')
// true

isWGS84Projection('EPSG:3857')
// false

isWGS84Projection('EPSG:2154')
// false

isWGS84Projection('UNKNOWN')
// false