Class: QgsCoordinateReferenceSystem¶
-
class
qgis.core.
QgsCoordinateReferenceSystem
¶ Bases:
sip.wrapper
Constructs an invalid CRS object
QgsCoordinateReferenceSystem(definition: str) 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() - “PROJ4:<proj4>” - handled with createFromProj4() - “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()
/ // TODO QGIS 3: remove “POSTGIS” and “INTERNAL”, allow PROJ4 without the prefixQgsCoordinateReferenceSystem(id: int, type: QgsCoordinateReferenceSystem.CrsType = QgsCoordinateReferenceSystem.PostgisCrsId) 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, WKT or Proj4 to describe CRS’s in your code wherever possible. Internal QGIS CRS IDs are not guaranteed to be permanent / involatile.
- Parameters
id – The ID valid for the chosen CRS ID type
type – One of the types described in CrsType / // TODO QGIS 3: remove type and always use EPSG code
QgsCoordinateReferenceSystem(srs:
QgsCoordinateReferenceSystem
) Copy constructorThis 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:
1. 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). 2. 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 proj4 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(), toProj4(), mapUnits() and others. Creation of CRS instances is further described in ref crs_construct_and_copy 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.toProj4())) 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]
This section gives an overview of various supported CRS definition formats:
1. 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 authid() and createFromOgcWmsCrs() methods.
2. 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 proj4 library. For example, the definition of WGS84 looks like this:
+proj=longlat +datum=WGS84 +no_defs
See toProj4() and createFromProj4() methods.
3. 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 toWkt() and createFromWkt() methods.
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 ref 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.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).
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.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
Methods
Returns the authority identifier for the CRS.
Returns the approximate bounds for the region the CRS is usable within.
Sets this CRS by lookup of the given ID in the CRS database.
Sets this CRS to the given OGC WMS-format Coordinate Reference Systems.
Sets this CRS by passing it a PROJ style formatted string.
Sets this CRS by lookup of the given PostGIS SRID in the CRS database.
Sets this CRS by lookup of internal QGIS CRS ID in the CRS database.
Set up this CRS from a string definition.
Set up this CRS from various text formats.
Sets this CRS using a WKT definition.
Returns the descriptive name of the CRS, e.g., “WGS 84” or “GDA 94 / Vicgrid94”.
Returns the ellipsoid acronym for the ellipsoid used by the CRS.
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.
Creates a CRS from a given EPSG ID.
Creates a CRS from a given OGC WMS-format Coordinate Reference System string.
Creates a CRS from a proj4 style formatted string.
Creates a CRS from a specified QGIS SRS ID.
Creates a CRS from a WKT spatial ref sys definition string.
Returns auth id of related geographic CRS
Returns whether axis is inverted (e.g., for WMS 1.3) for the CRS.
Clears the internal cache used to initialize
QgsCoordinateReferenceSystem
objects.Returns whether the CRS is a geographic CRS (using lat/lon coordinates)
Returns whether this CRS is correctly initialized and usable
Returns the units for the projection used by the CRS.
Returns PostGIS SRID for the CRS.
Returns the projection acronym for the projection used by the CRS.
Restores state from the given DOM node.
Returns a list of recently used projections
Save the proj4-string as a custom CRS.
Set user hint for validation
Make sure that ESRI WKT import is done properly.
Returns the internal CRS ID, if available.
Update proj.4 parameters in our database from proj.4
Returns a Proj4 string representation of this CRS.
Returns a WKT representation of this CRS.
Returns a list of all valid SRS IDs present in the CRS database.
Perform some validation on this CRS.
Gets user hint for validation
Stores state to the given Dom node in the given document.
Attributes
-
class
CrsType
¶ Bases:
int
-
EpsgCrsId
= 2¶
-
InternalCrsId
= 0¶
-
PostgisCrsId
= 1¶
-
authid
(self) → str¶ 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”
- Return type
str
- Returns
the authority identifier for this CRS
See also
-
bounds
(self) → QgsRectangle¶ 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.
New in version 3.0.
- Return type
-
createFromId
(self, id: int, type: QgsCoordinateReferenceSystem.CrsType = QgsCoordinateReferenceSystem.PostgisCrsId) → bool¶ Sets this CRS by lookup of the given ID in the CRS database.
- Return type
bool
- Returns
True on success else false
Note
We encourage you to use EPSG code, WKT or Proj4 to describe CRS’s in your code wherever possible. Internal QGIS CRS IDs are not guaranteed to be permanent / involatile. / // TODO QGIS 3: remove type and always use EPSG code, rename to createFromEpsg
- Parameters
id (int) –
type (QgsCoordinateReferenceSystem.CrsType = QgsCoordinateReferenceSystem.PostgisCrsId) –
-
createFromOgcWmsCrs
(self, crs: str) → bool¶ 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.
- Return type
bool
- Returns
True on success else false
Note
this method uses an internal cache. Call invalidateCache() to clear the cache.
See also
fromOgcWmsCrs()
/ // TODO QGIS 3: remove “QGIS” and “CUSTOM”, only support “USER” (also returned by authid())- Parameters
crs (str) –
-
createFromProj4
(self, projString: str) → bool¶ 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 proj4 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 proj4 string to internal QGIS CRS ID using the following logic:
perform a whole text search on proj4 string (if not null)
if not match is found, split proj4 into individual parameters and try to find
a match where the parameters are in a different order - if none of the above match, use findMatchingProj()
- Parameters
projString (str) – A proj4 format string
- Return type
bool
- Returns
True on success else false
Note
Some members may be left blank if no match can be found in CRS database.
Note
this method uses an internal cache. Call invalidateCache() to clear the cache.
See also
-
createFromSrid
(self, srid: int) → bool¶ Sets this CRS by lookup of the given PostGIS SRID in the CRS database.
- Parameters
srid (int) – The PostGIS SRID for the desired spatial reference system.
- Return type
bool
- Returns
True on success else false / // TODO QGIS 3: remove unless really necessary - let’s use EPSG codes instead
-
createFromSrsId
(self, srsId: int) → bool¶ 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 (int) – The internal QGIS CRS ID for the desired spatial reference system.
- Return type
bool
- Returns
True on success else false
Note
this method uses an internal cache. Call invalidateCache() to clear the cache.
See also
-
createFromString
(self, definition: str) → bool¶ 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() - “PROJ4:<proj4>” - handled with createFromProj4() - “WKT:<wkt>” - handled with createFromWkt()
If no prefix is specified, WKT definition is assumed.
- Parameters
definition (str) – A String containing a coordinate reference system definition.
- Return type
bool
- Returns
True on success else false
-
createFromUserInput
(self, definition: str) → bool¶ 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() ( http://www.gdal.org/ogr/classOGRSpatialReference.html#aec3c6a49533fe457ddc763d699ff8796 )
- Parameters
definition (str) – A String containing a coordinate reference system definition.
- Return type
bool
- Returns
True on success else false
Note
this function generates a WKT string using OSRSetFromUserInput() and passes it to createFromWkt() function. / // TODO QGIS3: rename to createFromStringOGR so it is clear it’s similar to createFromString, just different backend
-
createFromWkt
(self, wkt: str) → bool¶ 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. Otherwise the WKT will be converted to a proj4 string and createFromProj4() set up the object.
- Parameters
wkt (str) – The WKT for the desired spatial reference system.
- Return type
bool
- Returns
True on success else false
Note
Some members may be left blank if no match can be found in CRS database.
Note
this method uses an internal cache. Call invalidateCache() to clear the cache.
See also
-
description
(self) → str¶ Returns the descriptive name of the CRS, e.g., “WGS 84” or “GDA 94 / Vicgrid94”. In most cases this is the best method to use when showing a friendly identifier for the CRS to a user.
- Return type
str
- Returns
descriptive name of the CRS
Note
an empty string will be returned if the description is not available for the CRS
See also
-
ellipsoidAcronym
(self) → str¶ Returns the ellipsoid acronym for the ellipsoid used by the CRS.
- Return type
str
- Returns
the official proj4 acronym for the ellipoid
Note
an empty string will be returned if the ellipsoidAcronym is not available for the CRS
See also
-
findMatchingProj
(self) → int¶ 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 proj4string!
- Return type
int
- Returns
long the SrsId of the matched CRS, zero if no match was found / // TODO QGIS 3: seems completely obsolete now (only compares proj4 - already done in createFromProj4)
-
fromEpsgId
(epsg: int) → QgsCoordinateReferenceSystem¶ Creates a CRS from a given EPSG ID.
- Parameters
epsg (int) – epsg CRS ID
- Return type
- Returns
matching CRS, or an invalid CRS if string could not be matched
New in version 3.0.
-
fromOgcWmsCrs
(ogcCrs: str) → QgsCoordinateReferenceSystem¶ Creates a CRS from a given OGC WMS-format Coordinate Reference System string.
- Parameters
ogcCrs (str) – OGR compliant CRS definition, e.g., “EPSG:4326”
- Return type
- Returns
matching CRS, or an invalid CRS if string could not be matched
See also
New in version 3.0.
-
fromProj4
(proj4: str) → QgsCoordinateReferenceSystem¶ Creates a CRS from a proj4 style formatted string.
- Parameters
proj4 (str) – proj4 format string
- Return type
- Returns
matching CRS, or an invalid CRS if string could not be matched
See also
New in version 3.0.
-
fromSrsId
(srsId: int) → QgsCoordinateReferenceSystem¶ Creates a CRS from a specified QGIS SRS ID.
- Parameters
srsId (int) – internal QGIS SRS ID
- Return type
- Returns
matching CRS, or an invalid CRS if ID could not be found
See also
See also
New in version 3.0.
-
fromWkt
(wkt: str) → QgsCoordinateReferenceSystem¶ Creates a CRS from a WKT spatial ref sys definition string.
- Parameters
wkt (str) – WKT for the desired spatial reference system.
- Return type
- Returns
matching CRS, or an invalid CRS if string could not be matched
See also
New in version 3.0.
-
geographicCrsAuthId
(self) → str¶ Returns auth id of related geographic CRS
- Return type
str
-
hasAxisInverted
(self) → bool¶ Returns whether axis is inverted (e.g., for WMS 1.3) for the CRS.
- Return type
bool
- Returns
true if CRS axis is inverted
-
invalidateCache
()¶ 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.New in version 3.0.
-
isGeographic
(self) → bool¶ Returns whether the CRS is a geographic CRS (using lat/lon coordinates)
- Return type
bool
- Returns
true if CRS is geographic, or false if it is a projected CRS
-
isValid
(self) → bool¶ Returns whether this CRS is correctly initialized and usable
- Return type
bool
-
mapUnits
(self) → QgsUnitTypes.DistanceUnit¶ Returns the units for the projection used by the CRS.
- Return type
-
postgisSrid
(self) → int¶ Returns PostGIS SRID for the CRS.
- Return type
int
- Returns
the PostGIS spatial_ref_sys identifier for this CRS (defaults to 0) / // TODO QGIS 3: remove unless really necessary - let’s use EPSG codes instead
-
projectionAcronym
(self) → str¶ Returns the projection acronym for the projection used by the CRS.
- Return type
str
- Returns
the official proj4 acronym for the projection family
Note
an empty string will be returned if the projectionAcronym is not available for the CRS
See also
-
readXml
(self, node: QDomNode) → bool¶ 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 (QDomNode) – The node from which state will be restored
- Return type
bool
- Returns
bool True on success, False on failure
-
recentProjections
() → List[str]¶ Returns a list of recently used projections
- Return type
List[str]
- Returns
list of srsid for recently used projections
New in version 2.7.
-
saveAsUserCrs
(self, name: str) → int¶ Save the proj4-string as a custom CRS.
Returns the new CRS srsid(), or -1 if the CRS could not be saved.
- Parameters
name (str) –
- Return type
int
-
setValidationHint
(self, html: str)¶ Set user hint for validation
- Parameters
html (str) –
-
setupESRIWktFix
()¶ 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.
Note
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() .
-
srsid
(self) → int¶ Returns the internal CRS ID, if available.
- Return type
int
- Returns
the internal sqlite3 srs.db primary key for this CRS
-
staticMetaObject
= <PyQt5.QtCore.QMetaObject object>¶
-
syncDatabase
() → int¶ Update proj.4 parameters in our database from proj.4
- Return type
int
- 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
-
toProj4
(self) → str¶ Returns a Proj4 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.
- Return type
str
- Returns
Proj4 format string that defines this CRS.
Note
an empty string will be returned if the CRS could not be represented by a Proj4 string
See also
-
toWkt
(self) → str¶ Returns a WKT representation of this CRS.
- Return type
str
- Returns
string containing WKT of the CRS
See also
-
validSrsIds
() → object¶ 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
New in version 3.0.
- Return type
object
-
validate
(self)¶ 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()
-
validationHint
(self) → str¶ Gets user hint for validation
- Return type
str
-
writeXml
(self, node: QDomNode, doc: QDomDocument) → bool¶ Stores state to the given Dom node in the given document.
- Parameters
node (QDomNode) – The node in which state will be restored
doc (QDomDocument) – The document in which state will be stored
- Return type
bool
- Returns
bool True on success, False on failure