This class represents a coordinate reference system (CRS). More...

#include <qgscoordinatereferencesystem.h>

Public Types
enum	CrsType { InternalCrsId , PostgisCrsId , EpsgCrsId }
	Enumeration of types of IDs accepted in createFromId() method. More...

enum	Format { FormatWkt = 0 , FormatProj }
	Projection definition formats. More...

enum	IdentifierType { ShortString , MediumString , FullString }
	Type of identifier string to create. More...

enum	WktVariant { WKT1_GDAL , WKT1_ESRI , WKT2_2015 , WKT2_2015_SIMPLIFIED , WKT2_2018 , WKT2_2018_SIMPLIFIED , WKT2_2019 = WKT2_2018 , WKT2_2019_SIMPLIFIED = WKT2_2018_SIMPLIFIED , WKT_PREFERRED = WKT2_2019 , WKT_PREFERRED_SIMPLIFIED = WKT2_2019_SIMPLIFIED , WKT_PREFERRED_GDAL = WKT2_2019 }
	WKT formatting variants, only used for builds based on Proj >= 6. More...

Public Member Functions
	QgsCoordinateReferenceSystem ()
	Constructs an invalid CRS object. More...

	QgsCoordinateReferenceSystem (const QgsCoordinateReferenceSystem &srs)
	Copy constructor. More...

	QgsCoordinateReferenceSystem (const QString &definition)
	Constructs a CRS object from a string definition using createFromString() More...

Q_DECL_DEPRECATED	QgsCoordinateReferenceSystem (long id, CrsType type=PostgisCrsId)
	Constructor. More...

	~QgsCoordinateReferenceSystem ()

QString	authid () const
	Returns the authority identifier for the CRS. More...

QgsRectangle	bounds () const
	Returns the approximate bounds for the region the CRS is usable within. More...

Q_DECL_DEPRECATED bool	createFromId (long id, CrsType type=PostgisCrsId)
	Sets this CRS by lookup of the given ID in the CRS database. More...

bool	createFromOgcWmsCrs (const QString &crs)
	Sets this CRS to the given OGC WMS-format Coordinate Reference Systems. More...

bool	createFromProj (const QString &projString, bool identify=true)
	Sets this CRS by passing it a PROJ style formatted string. More...

Q_DECL_DEPRECATED bool	createFromProj4 (const QString &projString)
	Sets this CRS by passing it a PROJ style formatted string. More...

Q_DECL_DEPRECATED bool	createFromSrid (long srid)
	Sets this CRS by lookup of the given PostGIS SRID in the CRS database. More...

bool	createFromSrsId (long srsId)
	Sets this CRS by lookup of internal QGIS CRS ID in the CRS database. More...

bool	createFromString (const QString &definition)
	Set up this CRS from a string definition. More...

bool	createFromUserInput (const QString &definition)
	Set up this CRS from various text formats. More...

bool	createFromWkt (const QString &wkt)
	Sets this CRS using a WKT definition. More...

QString	description () const
	Returns the descriptive name of the CRS, e.g., "WGS 84" or "GDA 94 / Vicgrid94". More...

QString	ellipsoidAcronym () const
	Returns the ellipsoid acronym for the ellipsoid used by the CRS. More...

Q_DECL_DEPRECATED long	findMatchingProj ()
	Walks the CRS databases (both system and user database) trying to match stored PROJ string to a database entry in order to fill in further pieces of information about CRS. More...

QString	geographicCrsAuthId () const
	Returns auth id of related geographic CRS. More...

bool	hasAxisInverted () const
	Returns whether axis is inverted (e.g., for WMS 1.3) for the CRS. More...

bool	isGeographic () const
	Returns whether the CRS is a geographic CRS (using lat/lon coordinates) More...

bool	isValid () const
	Returns whether this CRS is correctly initialized and usable. More...

QgsUnitTypes::DistanceUnit	mapUnits () const
	Returns the units for the projection used by the CRS. More...

	operator QVariant () const
	Allows direct construction of QVariants from QgsCoordinateReferenceSystem. More...

bool	operator!= (const QgsCoordinateReferenceSystem &srs) const
	Overloaded != operator used to compare to CRS's. More...

QgsCoordinateReferenceSystem &	operator= (const QgsCoordinateReferenceSystem &srs)
	Assignment operator. More...

bool	operator== (const QgsCoordinateReferenceSystem &srs) const
	Overloaded == operator used to compare to CRS's. More...

long	postgisSrid () const
	Returns PostGIS SRID for the CRS. More...

QString	projectionAcronym () const
	Returns the projection acronym for the projection used by the CRS. More...

bool	readXml (const QDomNode &node)
	Restores state from the given DOM node. More...

long	saveAsUserCrs (const QString &name, Format nativeFormat=FormatWkt)
	Saves the CRS as a new custom ("USER") CRS. More...

void	setValidationHint (const QString &html)
	Set user hint for validation. More...

long	srsid () const
	Returns the internal CRS ID, if available. More...

QString	toProj () const
	Returns a Proj string representation of this CRS. More...

Q_DECL_DEPRECATED QString	toProj4 () const
	Returns a Proj string representation of this CRS. More...

QString	toWkt (WktVariant variant=WKT1_GDAL, bool multiline=false, int indentationWidth=4) const
	Returns a WKT representation of this CRS. More...

void	updateDefinition ()
	Updates the definition and parameters of the coordinate reference system to their latest values. More...

QString	userFriendlyIdentifier (IdentifierType type=MediumString) const
	Returns a user friendly identifier for the CRS. More...

void	validate ()
	Perform some validation on this CRS. More...

QString	validationHint ()
	Gets user hint for validation. More...

bool	writeXml (QDomNode &node, QDomDocument &doc) const
	Stores state to the given Dom node in the given document. More...

Static Public Member Functions
static CUSTOM_CRS_VALIDATION	customCrsValidation ()
	Gets custom function. More...

static Q_INVOKABLE QgsCoordinateReferenceSystem	fromEpsgId (long epsg)
	Creates a CRS from a given EPSG ID. More...

static QgsCoordinateReferenceSystem	fromOgcWmsCrs (const QString &ogcCrs)
	Creates a CRS from a given OGC WMS-format Coordinate Reference System string. More...

static QgsCoordinateReferenceSystem	fromProj (const QString &proj)
	Creates a CRS from a proj style formatted string. More...

static Q_DECL_DEPRECATED QgsCoordinateReferenceSystem	fromProj4 (const QString &proj4)
	Creates a CRS from a proj style formatted string. More...

static QgsCoordinateReferenceSystem	fromSrsId (long srsId)
	Creates a CRS from a specified QGIS SRS ID. More...

static QgsCoordinateReferenceSystem	fromWkt (const QString &wkt)
	Creates a CRS from a WKT spatial ref sys definition string. More...

static void	invalidateCache (bool disableCache=false)
	Clears the internal cache used to initialize QgsCoordinateReferenceSystem objects. More...

static void	pushRecentCoordinateReferenceSystem (const QgsCoordinateReferenceSystem &crs)
	Pushes a recently used CRS to the top of the recent CRS list. More...

static QList< QgsCoordinateReferenceSystem >	recentCoordinateReferenceSystems ()
	Returns a list of recently used CRS. More...

static Q_DECL_DEPRECATED QStringList	recentProjections ()
	Returns a list of recently used projections. More...

static void	setCustomCrsValidation (CUSTOM_CRS_VALIDATION f)
	Sets custom function to force valid CRS. More...

static Q_DECL_DEPRECATED void	setupESRIWktFix ()
	Make sure that ESRI WKT import is done properly. More...

static int	syncDatabase ()
	Update proj.4 parameters in our database from proj.4. More...

static QList< long >	validSrsIds ()
	Returns a list of all valid SRS IDs present in the CRS database. More...

Properties
bool	isGeographic

Q_GADGET QgsUnitTypes::DistanceUnit	mapUnits

Friends
class	QgsCoordinateReferenceSystemRegistry

class	QgsPostgresProvider

class	TestQgsCoordinateReferenceSystem

Detailed Description

This class represents a coordinate reference system (CRS).

Coordinate reference system object defines a specific map projection, as well as transformations between different coordinate reference systems. There are various ways how a CRS can be defined: using well-known text (WKT), PROJ string or combination of authority and code (e.g. EPSG:4326). QGIS comes with its internal database of coordinate reference systems (stored in SQLite) that allows lookups of CRS and seamless conversions between the various definitions.

Most commonly one comes across two types of coordinate systems:

Geographic coordinate systems: based on a geodetic datum, normally with coordinates being latitude/longitude in degrees. The most common one is World Geodetic System 84 (WGS84).
Projected coordinate systems: based on a geodetic datum with coordinates projected to a plane, typically using meters or feet as units. Common projected coordinate systems are Universal Transverse Mercator or Albers Equal Area.

Internally QGIS uses proj library for all the math behind coordinate transformations, so in case of any troubles with projections it is best to examine the PROJ representation within the object, as that is the representation that will be ultimately used.

Methods that allow inspection of CRS instances include isValid(), authid(), description(), toWkt(), toProj(), mapUnits() and others. Creation of CRS instances is further described in Object Construction and Copying section below. Transformations between coordinate reference systems are done using QgsCoordinateTransform class.

For example, the following code will create and inspect "British national grid" CRS:

crs = QgsCoordinateReferenceSystem("EPSG:27700")
if crs.isValid():
    print("CRS Description: {}".format(crs.description()))
    print("CRS PROJ text: {}".format(crs.toProj()))
else:
    print("Invalid CRS!")

This will produce the following output:

CRS Description: OSGB 1936 / British National Grid

CRS PROJ text: +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 [output trimmed]

CRS Definition Formats

This section gives an overview of various supported CRS definition formats:

Authority and Code: Also referred to as OGC WMS format within QGIS as they have been widely used in OGC standards. These are encoded as <auth>:<code>, for example EPSG:4326 refers to WGS84 system. EPSG is the most commonly used authority that covers a wide range of coordinate systems around the world.

An extended variant of this format is OGC URN. Syntax of URN for CRS definition is urn:ogc:def:crs:<auth>:[<version>]:<code>. This class can also parse URNs (versions are currently ignored). For example, WGS84 may be encoded as urn:ogc:def:crs:OGC:1.3:CRS84.

QGIS adds support for "USER" authority that refers to IDs used internally in QGIS. This variant is best avoided or used with caution as the IDs are not permanent and they refer to different CRS on different machines or user profiles.

See also
authid()

createFromOgcWmsCrs()
PROJ string: This is a string consisting of a series of key/value pairs in the following format: +param1=value1 +param2=value2 [...]. This is the format natively used by the underlying proj library. For example, the definition of WGS84 looks like this:

+proj=longlat +datum=WGS84 +no_defs

See also: toProj(); createFromProj()

Well-known text (WKT): Defined by Open Geospatial Consortium (OGC), this is another common format to define CRS. For WGS84 the OGC WKT definition is the following:

GEOGCS["WGS 84",
       DATUM["WGS_1984",
         SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],
         AUTHORITY["EPSG","6326"]],
       PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
       UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],
       AUTHORITY["EPSG","4326"]]

See also: toWkt(); createFromWkt()

CRS Database and Custom CRS

The database of CRS shipped with QGIS is stored in a SQLite database (see QgsApplication::srsDatabaseFilePath()) and it is based on the data files maintained by GDAL project (a variety of .csv and .wkt files).

Sometimes it happens that users need to use a CRS definition that is not well known or that has been only created with a specific purpose (and thus its definition is not available in our database of CRS). Whenever a new CRS definition is seen, it will be added to the local database (in user's home directory, see QgsApplication::qgisUserDatabaseFilePath()). QGIS also features a GUI for management of local custom CRS definitions.

There are therefore two databases: one for shipped CRS definitions and one for custom CRS definitions. Custom CRS have internal IDs (accessible with srsid()) greater or equal to USER_CRS_START_ID. The local CRS databases should never be accessed directly with SQLite functions, instead you should use QgsCoordinateReferenceSystem API for CRS lookups and for managements of custom CRS.

Validation

In some cases (most prominently when loading a map layer), QGIS will try to ensure that the given map layer CRS is valid using validate() call. If not, a custom validation function will be called - such function may for example show a GUI for manual CRS selection. The validation function is configured using setCustomCrsValidation(). If validation fails or no validation function is set, the default CRS is assigned (WGS84). QGIS application registers its validation function that will act according to user's settings (either show CRS selector dialog or use project/custom CRS).

Object Construction and Copying

The easiest way of creating CRS instances is to use QgsCoordinateReferenceSystem(const QString&) constructor that automatically recognizes definition format from the given string.

Creation of CRS object involves some queries in a local SQLite database, which may be potentially expensive. Consequently, CRS creation methods use an internal cache to avoid unnecessary database lookups. If the CRS database is modified, then it is necessary to call invalidateCache() to ensure that outdated records are not being returned from the cache.

Since QGIS 2.16 QgsCoordinateReferenceSystem objects are implicitly shared.

Caveats

There are two different flavors of WKT: one is defined by OGC, the other is the standard used by ESRI. They look very similar, but they are not the same. QGIS is able to consume both flavors.

See also: QgsCoordinateTransform

Definition at line 209 of file qgscoordinatereferencesystem.h.

Member Enumeration Documentation

◆ CrsType

enum QgsCoordinateReferenceSystem::CrsType

Enumeration of types of IDs accepted in createFromId() method.

Enumerator
InternalCrsId	Internal ID used by QGIS in the local SQLite database.
PostgisCrsId	SRID used in PostGIS. DEPRECATED – DO NOT USE.
EpsgCrsId	EPSG code.

Definition at line 219 of file qgscoordinatereferencesystem.h.

◆ Format

enum QgsCoordinateReferenceSystem::Format

Projection definition formats.

Enumerator
FormatWkt	WKT format (always recommended over proj string format)
FormatProj	Proj string format.

Definition at line 227 of file qgscoordinatereferencesystem.h.

◆ IdentifierType

enum QgsCoordinateReferenceSystem::IdentifierType

Type of identifier string to create.

Since: QGIS 3.10.3

Enumerator
ShortString	A heavily abbreviated string, for use when a compact representation is required.
MediumString	A medium-length string, recommended for general purpose use.
FullString	Full definition – possibly a very lengthy string, e.g. with no truncation of custom WKT definitions.

Definition at line 633 of file qgscoordinatereferencesystem.h.

◆ WktVariant

enum QgsCoordinateReferenceSystem::WktVariant

WKT formatting variants, only used for builds based on Proj >= 6.

Enumerator
WKT1_GDAL	WKT1 as traditionally output by GDAL, deriving from OGC 01-009. A notable departure from WKT1_GDAL with respect to OGC 01-009 is that in WKT1_GDAL, the unit of the PRIMEM value is always degrees.
WKT1_ESRI	WKT1 as traditionally output by ESRI software, deriving from OGC 99-049.
WKT2_2015	Full WKT2 string, conforming to ISO 19162:2015(E) / OGC 12-063r5 with all possible nodes and new keyword names.
WKT2_2015_SIMPLIFIED	Same as WKT2_2015 with the following exceptions: UNIT keyword used. ID node only on top element. No ORDER element in AXIS element. PRIMEM node omitted if it is Greenwich. ELLIPSOID.UNIT node omitted if it is UnitOfMeasure::METRE. PARAMETER.UNIT / PRIMEM.UNIT omitted if same as AXIS. AXIS.UNIT omitted and replaced by a common GEODCRS.UNIT if they are all the same on all axis.
WKT2_2018	Alias for WKT2_2019.
WKT2_2018_SIMPLIFIED	Alias for WKT2_2019_SIMPLIFIED.
WKT2_2019	Full WKT2 string, conforming to ISO 19162:2019 / OGC 18-010, with all possible nodes and new keyword names. Non-normative list of differences: WKT2_2019 uses GEOGCRS / BASEGEOGCRS keywords for GeographicCRS.
WKT2_2019_SIMPLIFIED	WKT2_2019 with the simplification rule of WKT2_SIMPLIFIED.
WKT_PREFERRED	Preferred format, matching the most recent WKT ISO standard. Currently an alias to WKT2_2019, but may change in future versions.
WKT_PREFERRED_SIMPLIFIED	Preferred simplified format, matching the most recent WKT ISO standard. Currently an alias to WKT2_2019_SIMPLIFIED, but may change in future versions.
WKT_PREFERRED_GDAL	Preferred format for conversion of CRS to WKT for use with the GDAL library.

Definition at line 672 of file qgscoordinatereferencesystem.h.

Constructor & Destructor Documentation

◆ QgsCoordinateReferenceSystem() [1/4]

QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem ( )

Constructs an invalid CRS object.

Definition at line 113 of file qgscoordinatereferencesystem.cpp.

◆ ~QgsCoordinateReferenceSystem()

QgsCoordinateReferenceSystem::~QgsCoordinateReferenceSystem ( )

Definition at line 250 of file qgscoordinatereferencesystem.cpp.

◆ QgsCoordinateReferenceSystem() [2/4]

QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem ( const QString & definition )

explicit

Constructs a CRS object from a string definition using createFromString()

It supports the following formats:

"EPSG:<code>" - handled with createFromOgcWms()
"POSTGIS:<srid>" - handled with createFromSrid()
"INTERNAL:<srsid>" - handled with createFromSrsId()
"PROJ:<proj>" - handled with createFromProj()
"WKT:<wkt>" - handled with createFromWkt()

If no prefix is specified, WKT definition is assumed.

Parameters

definition A String containing a coordinate reference system definition.

See also: createFromString()

Definition at line 120 of file qgscoordinatereferencesystem.cpp.

◆ QgsCoordinateReferenceSystem() [3/4]

QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem	(	long	id,
		CrsType	type = `PostgisCrsId`
	)

explicit

Constructor.

A CRS object using a PostGIS SRID, an EPSG code or an internal QGIS CRS ID.

Note: We encourage you to use EPSG code or WKT to describe CRSes in your code wherever possible. Internal QGIS CRS IDs are not guaranteed to be permanent / involatile, and proj strings are a lossy format.

Parameters

id	The ID valid for the chosen CRS ID type
type	One of the types described in CrsType

Deprecated:: QGIS 3.10 We encourage you to use EPSG codes or WKT to describe CRSes in your code wherever possible. Internal QGIS CRS IDs are not guaranteed to be permanent / involatile, and Proj strings are a lossy format.

Definition at line 126 of file qgscoordinatereferencesystem.cpp.

◆ QgsCoordinateReferenceSystem() [4/4]

QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem ( const QgsCoordinateReferenceSystem & srs )

Copy constructor.

Definition at line 134 of file qgscoordinatereferencesystem.cpp.

Member Function Documentation

◆ authid()

QString QgsCoordinateReferenceSystem::authid ( ) const

Returns the authority identifier for the CRS.

The identifier includes both the authority (e.g., EPSG) and the CRS number (e.g., 4326). This is the best method to use when showing a very short CRS identifier to a user, e.g., "EPSG:4326".

If CRS object is a custom CRS (not found in database), the method will return internal QGIS CRS ID with "QGIS" authority, for example "QGIS:100005"

Returns: the authority identifier for this CRS

See also: description()

Definition at line 1324 of file qgscoordinatereferencesystem.cpp.

◆ bounds()

QgsRectangle QgsCoordinateReferenceSystem::bounds ( ) const

Returns the approximate bounds for the region the CRS is usable within.

The returned bounds represent the latitude and longitude extent for the projection in the WGS 84 CRS.

Since: QGIS 3.0

Definition at line 1459 of file qgscoordinatereferencesystem.cpp.

◆ createFromId()

bool QgsCoordinateReferenceSystem::createFromId	(	long	id,
		CrsType	type = `PostgisCrsId`
	)

Sets this CRS by lookup of the given ID in the CRS database.

Returns: true on success else false

Deprecated:: QGIS 3.10 We encourage you to use EPSG code or WKT to describe CRSes in your code wherever possible. Internal QGIS CRS IDs are not guaranteed to be permanent / involatile, and Proj strings are a lossy format.

Definition at line 254 of file qgscoordinatereferencesystem.cpp.

◆ createFromOgcWmsCrs()

bool QgsCoordinateReferenceSystem::createFromOgcWmsCrs ( const QString & crs )

Sets this CRS to the given OGC WMS-format Coordinate Reference Systems.

Accepts both "<auth>:<code>" format and OGC URN "urn:ogc:def:crs:<auth>:[<version>]:<code>". It also recognizes "QGIS", "USER", "CUSTOM" authorities, which all have the same meaning and refer to QGIS internal CRS IDs.

Returns: true on success else false

Note: this method uses an internal cache. Call invalidateCache() to clear the cache.

See also: fromOgcWmsCrs()

Definition at line 391 of file qgscoordinatereferencesystem.cpp.

◆ createFromProj()

bool QgsCoordinateReferenceSystem::createFromProj	(	const QString &	projString,
		bool	identify = `true`
	)

Sets this CRS by passing it a PROJ style formatted string.

The string will be parsed and the projection and ellipsoid members set and the remainder of the Proj string will be stored in the parameters member. The reason for this is so that we can easily present the user with 'natural language' representation of the projection and ellipsoid by looking them up in the srs.db sqlite database.

We try to match the Proj string to internal QGIS CRS ID using the following logic:

ask the Proj library to identify the CRS to a standard registered CRS (e.g. EPSG codes)
if no match is found, compare the CRS to all user CRSes, using the Proj library to determine CRS equivalence (hence making the match parameter order insensitive)
if none of the above match, use the Proj string to create the CRS and do not associated an internal CRS ID to it.

Parameters

projString	A Proj format string
identify	if `false`, no attempts will be made to match the proj string against known CRS authorities. This is much faster, but should only ever be used when it is known in advance that the definition does not correspond to a known or user CRS. This argument is not available in Python.

Returns: true on success else false

Note: Some members may be left blank if no match can be found in CRS database.; This method uses an internal cache. Call invalidateCache() to clear the cache.

See also: fromProj()

Since: QGIS 3.10.3

Definition at line 937 of file qgscoordinatereferencesystem.cpp.

◆ createFromProj4()

bool QgsCoordinateReferenceSystem::createFromProj4 ( const QString & projString )

Sets this CRS by passing it a PROJ style formatted string.

The string will be parsed and the projection and ellipsoid members set and the remainder of the Proj string will be stored in the parameters member. The reason for this is so that we can easily present the user with 'natural language' representation of the projection and ellipsoid by looking them up in the srs.db sqlite database.

We try to match the Proj string to internal QGIS CRS ID using the following logic:

ask the Proj library to identify the CRS to a standard registered CRS (e.g. EPSG codes)
if no match is found, compare the CRS to all user CRSes, using the Proj library to determine CRS equivalence (hence making the match parameter order insensitive)
if none of the above match, use the Proj string to create the CRS and do not associated an internal CRS ID to it.

Parameters

projString A Proj format string

Returns: true on success else false

Note: Some members may be left blank if no match can be found in CRS database.; This method uses an internal cache. Call invalidateCache() to clear the cache.

See also: fromProj()

Deprecated:: QGIS 3.10 Use createFromProj() instead

Definition at line 932 of file qgscoordinatereferencesystem.cpp.

◆ createFromSrid()

bool QgsCoordinateReferenceSystem::createFromSrid ( long srid )

Sets this CRS by lookup of the given PostGIS SRID in the CRS database.

Parameters

srid	The PostGIS SRID for the desired spatial reference system.

Returns: true on success else false

Deprecated:: QGIS 3.10 Use alternative methods for SRS construction instead – this method was specifically created for use by the postgres provider alone, and using it elsewhere will lead to subtle bugs.

Definition at line 514 of file qgscoordinatereferencesystem.cpp.

◆ createFromSrsId()

bool QgsCoordinateReferenceSystem::createFromSrsId ( long srsId )

Sets this CRS by lookup of internal QGIS CRS ID in the CRS database.

If the srsid is < USER_CRS_START_ID, system CRS database is used, otherwise user's local CRS database from home directory is used.

Parameters

srsId The internal QGIS CRS ID for the desired spatial reference system.

Returns: true on success else false

Note: this method uses an internal cache. Call invalidateCache() to clear the cache.

See also: fromSrsId()

Warning: This method is highly discouraged, and CRS objects should instead be constructed using auth:id codes or WKT strings

Definition at line 564 of file qgscoordinatereferencesystem.cpp.

◆ createFromString()

bool QgsCoordinateReferenceSystem::createFromString ( const QString & definition )

Set up this CRS from a string definition.

It supports the following formats:

"EPSG:<code>" - handled with createFromOgcWms()
"POSTGIS:<srid>" - handled with createFromSrid()
"INTERNAL:<srsid>" - handled with createFromSrsId()
"PROJ:<proj>" - handled with createFromProj()
"WKT:<wkt>" - handled with createFromWkt()

If no prefix is specified, WKT definition is assumed.

Parameters

definition A String containing a coordinate reference system definition.

Returns: true on success else false

Definition at line 275 of file qgscoordinatereferencesystem.cpp.

◆ createFromUserInput()

bool QgsCoordinateReferenceSystem::createFromUserInput ( const QString & definition )

Set up this CRS from various text formats.

Valid formats: WKT string, "EPSG:n", "EPSGA:n", "AUTO:proj_id,unit_id,lon0,lat0", "urn:ogc:def:crs:EPSG::n", PROJ string, filename (with WKT, XML or PROJ string), well known name (such as NAD27, NAD83, WGS84 or WGS72), ESRI::[WKT string] (directly or in a file), "IGNF:xxx"

For more details on supported formats see OGRSpatialReference::SetFromUserInput() ( https://gdal.org/doxygen/classOGRSpatialReference.html#aec3c6a49533fe457ddc763d699ff8796 )

Parameters

definition A String containing a coordinate reference system definition.

Returns: true on success else false

Note: this function generates a WKT string using OSRSetFromUserInput() and passes it to createFromWkt() function.

Definition at line 343 of file qgscoordinatereferencesystem.cpp.

◆ createFromWkt()

bool QgsCoordinateReferenceSystem::createFromWkt ( const QString & wkt )

Sets this CRS using a WKT definition.

If EPSG code of the WKT definition can be determined, it is extracted and createFromOgcWmsCrs() is used to initialize the object.

Parameters

wkt	The WKT for the desired spatial reference system.

Returns: true on success else false

Note: Some members may be left blank if no match can be found in CRS database.; this method uses an internal cache. Call invalidateCache() to clear the cache.

See also: fromWkt()

Definition at line 847 of file qgscoordinatereferencesystem.cpp.

◆ customCrsValidation()

CUSTOM_CRS_VALIDATION QgsCoordinateReferenceSystem::customCrsValidation ( )

static

Gets custom function.

Note: not available in Python bindings

Definition at line 2283 of file qgscoordinatereferencesystem.cpp.

◆ description()

QString QgsCoordinateReferenceSystem::description ( ) const

Returns the descriptive name of the CRS, e.g., "WGS 84" or "GDA 94 / Vicgrid94".

Note: an empty string will be returned if the description is not available for the CRS

See also: authid(); userFriendlyIdentifier()

Definition at line 1329 of file qgscoordinatereferencesystem.cpp.

◆ ellipsoidAcronym()

QString QgsCoordinateReferenceSystem::ellipsoidAcronym ( ) const

Returns the ellipsoid acronym for the ellipsoid used by the CRS.

Returns: the official authority:code identifier for the ellipsoid, or PARAMETER:MAJOR:MINOR for custom ellipsoids

Note: an empty string will be returned if the ellipsoidAcronym is not available for the CRS

See also: projectionAcronym()

Definition at line 1376 of file qgscoordinatereferencesystem.cpp.

◆ findMatchingProj()

long QgsCoordinateReferenceSystem::findMatchingProj ( )

Walks the CRS databases (both system and user database) trying to match stored PROJ string to a database entry in order to fill in further pieces of information about CRS.

Note: The ellipsoid and projection acronyms must be set as well as the proj string!

Returns: long the SrsId of the matched CRS, zero if no match was found

Deprecated:: QGIS 3.10 Not used in Proj >= 6 based builds

Definition at line 1874 of file qgscoordinatereferencesystem.cpp.

◆ fromEpsgId()

QgsCoordinateReferenceSystem QgsCoordinateReferenceSystem::fromEpsgId ( long epsg )

static

Creates a CRS from a given EPSG ID.

Parameters

epsg	epsg CRS ID

Returns: matching CRS, or an invalid CRS if string could not be matched

Since: QGIS 3.0

Definition at line 210 of file qgscoordinatereferencesystem.cpp.

◆ fromOgcWmsCrs()

QgsCoordinateReferenceSystem QgsCoordinateReferenceSystem::fromOgcWmsCrs ( const QString & ogcCrs )

static

Creates a CRS from a given OGC WMS-format Coordinate Reference System string.

Parameters

ogcCrs OGR compliant CRS definition, e.g., "EPSG:4326"

Returns: matching CRS, or an invalid CRS if string could not be matched

See also: createFromOgcWmsCrs()

Since: QGIS 3.0

Definition at line 203 of file qgscoordinatereferencesystem.cpp.

◆ fromProj()

QgsCoordinateReferenceSystem QgsCoordinateReferenceSystem::fromProj ( const QString & proj )

static

Creates a CRS from a proj style formatted string.

Parameters

proj	proj format string

Returns: matching CRS, or an invalid CRS if string could not be matched

See also: createFromProj()

Since: QGIS 3.10.3

Definition at line 229 of file qgscoordinatereferencesystem.cpp.

◆ fromProj4()

QgsCoordinateReferenceSystem QgsCoordinateReferenceSystem::fromProj4 ( const QString & proj4 )

static

Creates a CRS from a proj style formatted string.

Returns: matching CRS, or an invalid CRS if string could not be matched

See also: createFromProj()

Deprecated:: QGIS 3.10 Use fromProj() instead.

Definition at line 224 of file qgscoordinatereferencesystem.cpp.

◆ fromSrsId()

QgsCoordinateReferenceSystem QgsCoordinateReferenceSystem::fromSrsId ( long srsId )

static

Creates a CRS from a specified QGIS SRS ID.

Parameters

srsId internal QGIS SRS ID

Returns: matching CRS, or an invalid CRS if ID could not be found

See also: createFromSrsId(); validSrsIds()

Since: QGIS 3.0

Definition at line 243 of file qgscoordinatereferencesystem.cpp.

◆ fromWkt()

QgsCoordinateReferenceSystem QgsCoordinateReferenceSystem::fromWkt ( const QString & wkt )

static

Creates a CRS from a WKT spatial ref sys definition string.

Parameters

wkt	WKT for the desired spatial reference system.

Returns: matching CRS, or an invalid CRS if string could not be matched

See also: createFromWkt()

Since: QGIS 3.0

Definition at line 236 of file qgscoordinatereferencesystem.cpp.

◆ geographicCrsAuthId()

QString QgsCoordinateReferenceSystem::geographicCrsAuthId ( ) const

Returns auth id of related geographic CRS.

Definition at line 3503 of file qgscoordinatereferencesystem.cpp.

◆ hasAxisInverted()

bool QgsCoordinateReferenceSystem::hasAxisInverted ( ) const

Returns whether axis is inverted (e.g., for WMS 1.3) for the CRS.

Returns: true if CRS axis is inverted

Definition at line 816 of file qgscoordinatereferencesystem.cpp.

◆ invalidateCache()

void QgsCoordinateReferenceSystem::invalidateCache ( bool disableCache = false )

static

Clears the internal cache used to initialize QgsCoordinateReferenceSystem objects.

This should be called whenever the srs database has been modified in order to ensure that outdated CRS objects are not created.

If disableCache is true then the inbuilt cache will be completely disabled. This argument is for internal use only.

Since: QGIS 3.0

Definition at line 3608 of file qgscoordinatereferencesystem.cpp.

◆ isGeographic()

bool QgsCoordinateReferenceSystem::isGeographic ( ) const

Returns whether the CRS is a geographic CRS (using lat/lon coordinates)

Returns: true if CRS is geographic, or false if it is a projected CRS

Definition at line 1446 of file qgscoordinatereferencesystem.cpp.

◆ isValid()

bool QgsCoordinateReferenceSystem::isValid ( ) const

Returns whether this CRS is correctly initialized and usable.

Definition at line 927 of file qgscoordinatereferencesystem.cpp.

◆ mapUnits()

QgsUnitTypes::DistanceUnit QgsCoordinateReferenceSystem::mapUnits ( ) const

Returns the units for the projection used by the CRS.

Definition at line 1451 of file qgscoordinatereferencesystem.cpp.

◆ operator QVariant()

QgsCoordinateReferenceSystem::operator QVariant ( ) const

inline

Allows direct construction of QVariants from QgsCoordinateReferenceSystem.

Definition at line 279 of file qgscoordinatereferencesystem.h.

◆ operator!=()

bool QgsCoordinateReferenceSystem::operator!= ( const QgsCoordinateReferenceSystem & srs ) const

Overloaded != operator used to compare to CRS's.

Returns opposite bool value to operator ==

Definition at line 1974 of file qgscoordinatereferencesystem.cpp.

◆ operator=()

QgsCoordinateReferenceSystem & QgsCoordinateReferenceSystem::operator= ( const QgsCoordinateReferenceSystem & srs )

Assignment operator.

Definition at line 140 of file qgscoordinatereferencesystem.cpp.

◆ operator==()

bool QgsCoordinateReferenceSystem::operator== ( const QgsCoordinateReferenceSystem & srs ) const

Overloaded == operator used to compare to CRS's.

Internally it will use authid() for comparison.

Definition at line 1950 of file qgscoordinatereferencesystem.cpp.

◆ postgisSrid()

long QgsCoordinateReferenceSystem::postgisSrid ( ) const

Returns PostGIS SRID for the CRS.

Returns: the PostGIS spatial_ref_sys identifier for this CRS (defaults to 0)

Definition at line 1319 of file qgscoordinatereferencesystem.cpp.

◆ projectionAcronym()

QString QgsCoordinateReferenceSystem::projectionAcronym ( ) const

Returns the projection acronym for the projection used by the CRS.

Returns: the official Proj acronym for the projection family

Note: an empty string will be returned if the projectionAcronym is not available for the CRS

See also: ellipsoidAcronym()

Definition at line 1364 of file qgscoordinatereferencesystem.cpp.

◆ pushRecentCoordinateReferenceSystem()

void QgsCoordinateReferenceSystem::pushRecentCoordinateReferenceSystem ( const QgsCoordinateReferenceSystem & crs )

static

Pushes a recently used CRS to the top of the recent CRS list.

Since: QGIS 3.10.3

Definition at line 3577 of file qgscoordinatereferencesystem.cpp.

◆ readXml()

bool QgsCoordinateReferenceSystem::readXml ( const QDomNode & node )

Restores state from the given DOM node.

If it fails or if the node is empty, a default empty CRS will be returned.

Parameters

node	The node from which state will be restored

Returns: bool true on success, false on failure

Definition at line 2043 of file qgscoordinatereferencesystem.cpp.

◆ recentCoordinateReferenceSystems()

QList< QgsCoordinateReferenceSystem > QgsCoordinateReferenceSystem::recentCoordinateReferenceSystems ( )

static

Returns a list of recently used CRS.

Since: QGIS 3.10.3

Definition at line 3546 of file qgscoordinatereferencesystem.cpp.

◆ recentProjections()

QStringList QgsCoordinateReferenceSystem::recentProjections ( )

static

Returns a list of recently used projections.

Returns: list of srsid for recently used projections

Deprecated:: QGIS 3.10 Use recentCoordinateReferenceSystems() instead.

Definition at line 3534 of file qgscoordinatereferencesystem.cpp.

◆ saveAsUserCrs()

long QgsCoordinateReferenceSystem::saveAsUserCrs	(	const QString &	name,
		Format	nativeFormat = `FormatWkt`
	)

Saves the CRS as a new custom ("USER") CRS.

Returns the new CRS srsid(), or -1 if the CRS could not be saved.

The nativeFormat argument specifies the format to use when saving the CRS definition. FormatWkt is recommended as it is a lossless format.

Warning: Not all CRS definitions can be represented as a Proj string, so take care when using the FormatProj option.

Note: Since QGIS 3.18, internally this calls QgsCoordinateReferenceSystemRegistry::addUserCrs().

Definition at line 2320 of file qgscoordinatereferencesystem.cpp.

◆ setCustomCrsValidation()

void QgsCoordinateReferenceSystem::setCustomCrsValidation ( CUSTOM_CRS_VALIDATION f )

static

Sets custom function to force valid CRS.

Note: not available in Python bindings

Definition at line 2278 of file qgscoordinatereferencesystem.cpp.

◆ setupESRIWktFix()

void QgsCoordinateReferenceSystem::setupESRIWktFix ( )

static

Make sure that ESRI WKT import is done properly.

This is required for proper shapefile CRS import when using gdal>= 1.9.

Note: This function is called by createFromUserInput() and QgsOgrProvider::crs(), there is usually no need to call it from elsewhere.; This function sets CPL config option GDAL_FIX_ESRI_WKT to a proper value, unless it has been set by the user through the commandline or an environment variable. For more details refer to OGRSpatialReference::morphFromESRI() .

Deprecated:: QGIS 3.10 Not used on builds based on Proj version 6 or later

Definition at line 370 of file qgscoordinatereferencesystem.cpp.

◆ setValidationHint()

void QgsCoordinateReferenceSystem::setValidationHint ( const QString & html )

Set user hint for validation.

Definition at line 2310 of file qgscoordinatereferencesystem.cpp.

◆ srsid()

long QgsCoordinateReferenceSystem::srsid ( ) const

Returns the internal CRS ID, if available.

Returns: the internal sqlite3 srs.db primary key for this CRS

Definition at line 1314 of file qgscoordinatereferencesystem.cpp.

◆ syncDatabase()

int QgsCoordinateReferenceSystem::syncDatabase ( )

static

Update proj.4 parameters in our database from proj.4.

Returns: number of updated CRS on success and negative number of failed updates in case of errors.

Note: This is used internally and should not be necessary to call in client code

Definition at line 2696 of file qgscoordinatereferencesystem.cpp.

◆ toProj()

QString QgsCoordinateReferenceSystem::toProj ( ) const

Returns a Proj string representation of this CRS.

If proj and ellps keys are found in the parameters, they will be stripped out and the projection and ellipsoid acronyms will be overridden with these.

Returns: Proj format string that defines this CRS.

Warning: Not all CRS definitions can be represented by Proj strings. An empty string will be returned if the CRS could not be represented by a Proj string.

See also: toWkt()

Since: QGIS 3.10.3

Definition at line 1423 of file qgscoordinatereferencesystem.cpp.

◆ toProj4()

QString QgsCoordinateReferenceSystem::toProj4 ( ) const

Returns a Proj string representation of this CRS.

If proj and ellps keys are found in the parameters, they will be stripped out and the projection and ellipsoid acronyms will be overridden with these.

Returns: Proj format string that defines this CRS.

Warning: Not all CRS definitions can be represented by Proj strings. An empty string will be returned if the CRS could not be represented by a Proj string.

See also: toWkt()

Deprecated:: QGIS 3.10 Use toProj() instead.

Definition at line 1418 of file qgscoordinatereferencesystem.cpp.

◆ toWkt()

QString QgsCoordinateReferenceSystem::toWkt	(	WktVariant	variant = `WKT1_GDAL`,
		bool	multiline = `false`,
		int	indentationWidth = `4`
	)		const

Returns a WKT representation of this CRS.

The variant argument specifies the formatting variant to use when creating the WKT string. This is only used on builds based on Proj >= 6, with earlier versions always using WKT1_GDAL.

If multiline is true then a formatted multiline string will be returned, using the specified indentationWidth. This is only used on builds based on Proj >= 6.

See also: toProj()

Definition at line 1979 of file qgscoordinatereferencesystem.cpp.

◆ updateDefinition()

void QgsCoordinateReferenceSystem::updateDefinition ( )

Updates the definition and parameters of the coordinate reference system to their latest values.

This only has an effect if the CRS is a user defined custom CRS, and the definition of that custom CRS has changed. In this case the parameters of the object (such as the proj and WKT string definitions, and other related properties) will be updated to reflect the current definition of the custom CRS.

Any objects which store CRS objects should connect to the QgsApplication::coordinateReferenceSystemRegistry()'s QgsCoordinateReferenceSystemRegistry::userCrsChanged() signal and call this method on their stored CRS objects whenever the signal is emitted in order to update these CRSes to their new definitions.

Since: QGIS 3.18

Definition at line 1525 of file qgscoordinatereferencesystem.cpp.

◆ userFriendlyIdentifier()

QString QgsCoordinateReferenceSystem::userFriendlyIdentifier ( IdentifierType type = MediumString ) const

Returns a user friendly identifier for the CRS.

Depending on the format of the CRS, this may reflect the CRSes registered name, or for CRSes not saved in the database it may reflect the underlying WKT or Proj string definition of the CRS.

In most cases this is the best method to use when showing a friendly identifier for the CRS to a user.

See also: description()

Since: QGIS 3.10.3

Definition at line 1341 of file qgscoordinatereferencesystem.cpp.

◆ validate()

void QgsCoordinateReferenceSystem::validate ( )

Perform some validation on this CRS.

If the CRS doesn't validate the default behavior settings for layers with unknown CRS will be consulted and acted on accordingly. By hell or high water this method will do its best to make sure that this CRS is valid - even if that involves resorting to a hard coded default of geocs:wgs84.

Note: It is not usually necessary to use this function, unless you are trying to force this CRS to be valid.

See also: setCustomCrsValidation(), customCrsValidation()

Definition at line 504 of file qgscoordinatereferencesystem.cpp.

◆ validationHint()

QString QgsCoordinateReferenceSystem::validationHint ( )

Gets user hint for validation.

Definition at line 2315 of file qgscoordinatereferencesystem.cpp.

◆ validSrsIds()

QList< long > QgsCoordinateReferenceSystem::validSrsIds ( )

static

Returns a list of all valid SRS IDs present in the CRS database.

Any of the returned values can be safely passed to fromSrsId() to create a new, valid QgsCoordinateReferenceSystem object.

See also: fromSrsId()

Since: QGIS 3.0

Definition at line 147 of file qgscoordinatereferencesystem.cpp.

◆ writeXml()

bool QgsCoordinateReferenceSystem::writeXml	(	QDomNode &	node,
		QDomDocument &	doc
	)		const

Stores state to the given Dom node in the given document.

Parameters

node	The node in which state will be restored
doc	The document in which state will be stored

Returns: bool true on success, false on failure

Definition at line 2148 of file qgscoordinatereferencesystem.cpp.

Friends And Related Function Documentation

◆ QgsCoordinateReferenceSystemRegistry

friend class QgsCoordinateReferenceSystemRegistry

friend

Definition at line 1001 of file qgscoordinatereferencesystem.h.

◆ QgsPostgresProvider

friend class QgsPostgresProvider

friend

Definition at line 1000 of file qgscoordinatereferencesystem.h.

◆ TestQgsCoordinateReferenceSystem

friend class TestQgsCoordinateReferenceSystem

friend

Definition at line 999 of file qgscoordinatereferencesystem.h.

Property Documentation

◆ isGeographic

bool QgsCoordinateReferenceSystem::isGeographic

read

Definition at line 211 of file qgscoordinatereferencesystem.h.

◆ mapUnits

Q_GADGET QgsUnitTypes::DistanceUnit QgsCoordinateReferenceSystem::mapUnits

read

Definition at line 211 of file qgscoordinatereferencesystem.h.

The documentation for this class was generated from the following files:

/build/qgis-3.18.1+99unstable/src/core/qgscoordinatereferencesystem.h
/build/qgis-3.18.1+99unstable/src/core/qgscoordinatereferencesystem.cpp

Public Types

Public Member Functions

Static Public Member Functions

Properties

Friends

Detailed Description

CRS Definition Formats

CRS Database and Custom CRS

Validation

Object Construction and Copying

Caveats

Member Enumeration Documentation

◆ CrsType

◆ Format

◆ IdentifierType

◆ WktVariant

Constructor & Destructor Documentation

◆ QgsCoordinateReferenceSystem() [1/4]

◆ ~QgsCoordinateReferenceSystem()

◆ QgsCoordinateReferenceSystem() [2/4]

◆ QgsCoordinateReferenceSystem() [3/4]

◆ QgsCoordinateReferenceSystem() [4/4]

Member Function Documentation

◆ authid()

◆ bounds()

◆ createFromId()

◆ createFromOgcWmsCrs()

◆ createFromProj()

◆ createFromProj4()

◆ createFromSrid()

◆ createFromSrsId()

◆ createFromString()

◆ createFromUserInput()

◆ createFromWkt()

◆ customCrsValidation()

◆ description()

◆ ellipsoidAcronym()

◆ findMatchingProj()

◆ fromEpsgId()

◆ fromOgcWmsCrs()

◆ fromProj()

◆ fromProj4()

◆ fromSrsId()

◆ fromWkt()

◆ geographicCrsAuthId()

◆ hasAxisInverted()

◆ invalidateCache()

◆ isGeographic()

◆ isValid()

◆ mapUnits()

◆ operator QVariant()

◆ operator!=()

◆ operator=()

◆ operator==()

◆ postgisSrid()

◆ projectionAcronym()

◆ pushRecentCoordinateReferenceSystem()

◆ readXml()

◆ recentCoordinateReferenceSystems()

◆ recentProjections()

◆ saveAsUserCrs()

◆ setCustomCrsValidation()

◆ setupESRIWktFix()

◆ setValidationHint()

◆ srsid()

◆ syncDatabase()

◆ toProj()

◆ toProj4()

◆ toWkt()

◆ updateDefinition()

◆ userFriendlyIdentifier()

◆ validate()

◆ validationHint()

◆ validSrsIds()

◆ writeXml()

Friends And Related Function Documentation

◆ QgsCoordinateReferenceSystemRegistry

◆ QgsPostgresProvider

◆ TestQgsCoordinateReferenceSystem

Property Documentation