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QgsCoordinateReferenceSystem Class Reference

Class for storing a coordinate reference system (CRS) More...

#include <qgscoordinatereferencesystem.h>

Public Types

enum  CrsType { InternalCrsId, PostgisCrsId, EpsgCrsId }

Public Member Functions

 QgsCoordinateReferenceSystem ()
 Default constructor.
 ~QgsCoordinateReferenceSystem ()
 QgsCoordinateReferenceSystem (QString theDefinition)
 QgsCoordinateReferenceSystem (const long theId, CrsType theType=PostgisCrsId)
 QgsCoordinateReferenceSystem (const QgsCoordinateReferenceSystem &srs)
 copy constructor
QgsCoordinateReferenceSystemoperator= (const QgsCoordinateReferenceSystem &srs)
 Assignment operator.
bool createFromId (const long theId, CrsType theType=PostgisCrsId)
bool createFromOgcWmsCrs (QString theCrs)
 Set up this CRS from the given OGC CRS.
bool createFromSrid (const long theSrid)
bool createFromWkt (const QString &theWkt)
bool createFromSrsId (const long theSrsId)
bool createFromProj4 (const QString &theProjString)
bool createFromString (const QString &theDefinition)
bool createFromUserInput (const QString &theDefinition)
bool isValid () const
void validate ()
long findMatchingProj ()
bool operator== (const QgsCoordinateReferenceSystem &theSrs) const
bool operator!= (const QgsCoordinateReferenceSystem &theSrs) const
bool readXML (QDomNode &theNode)
bool writeXML (QDomNode &theNode, QDomDocument &theDoc) const
long srsid () const
long postgisSrid () const
QString authid () const
QString description () const
QString projectionAcronym () const
QString ellipsoidAcronym () const
QString toWkt () const
QString toProj4 () const
 Get the Proj Proj4 string representation of this srs.
bool geographicFlag () const
bool axisInverted () const
QGis::UnitType mapUnits () const
void setValidationHint (QString html)
QString validationHint ()
bool saveAsUserCRS (QString name)
 Copied from QgsCustomProjectionDialog /// Please refactor into SQL handler !!! ///.
QString geographicCRSAuthId () const
 Returns auth id of related geographic CRS.

Static Public Member Functions

static void setupESRIWktFix ()
static void setCustomSrsValidation (CUSTOM_CRS_VALIDATION f)
 Sets custom function to force valid CRS QGIS uses implementation in QgisGui::customSrsValidation.
static CUSTOM_CRS_VALIDATION customSrsValidation ()
 Gets custom function.
static int syncDb ()

Detailed Description

Class for storing a coordinate reference system (CRS)

Member Enumeration Documentation

Enumerator:
InternalCrsId 
PostgisCrsId 
EpsgCrsId 

Constructor & Destructor Documentation

QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem ( )

Default constructor.

QgsCoordinateReferenceSystem::~QgsCoordinateReferenceSystem ( )
QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem ( QString  theDefinition)
explicit

Constructs a CRS object from a string definition as defined in the createFromString member function (by default a WKT definition).

Parameters
theDefinitionA String containing a coordinate reference system definition.
QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem ( const long  theId,
CrsType  theType = PostgisCrsId 
)

Use this constructor when you want to create a CRS object using a postgis SRID, an EpsgCrsId id or a QGIS CRS_ID.

Note
We encourage you to use EpsgCrsId, Wkt or Proj4 to describe CRS's in your code wherever possible. QGSI CRS_IDs are not guaranteed to be permanent / involatile.
Parameters
theIdThe ID no valid for the chosen coordinate system id type
theTypeOne of the types described in QgsCoordinateReferenceSystem::CrsType
QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem ( const QgsCoordinateReferenceSystem srs)

copy constructor

Member Function Documentation

QString QgsCoordinateReferenceSystem::authid ( ) const

Get the authority identifier for this srs

Returns
QString the Authority identifier for this srs
Note
added in 1.5
bool QgsCoordinateReferenceSystem::axisInverted ( ) const

return if axis is inverted (eg. for WMS 1.3)

Returns
bool Whether this is crs axis is inverted
Note
added in 1.8
bool QgsCoordinateReferenceSystem::createFromId ( const long  theId,
CrsType  theType = PostgisCrsId 
)
bool QgsCoordinateReferenceSystem::createFromOgcWmsCrs ( QString  theCrs)

Set up this CRS from the given OGC CRS.

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

Return values
falseif not given an valid label
bool QgsCoordinateReferenceSystem::createFromProj4 ( const QString &  theProjString)

Set up this srs by passing it a proj4 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.bs sqlite database. Also having the ellipse and proj elements stripped out is helpful to speed up globbing queries (see below).

We try to match the proj string to and srsid using the following logic:

  • perform a whole text search on srs name (if not null). The srs name will have been set if this method has been delegated to from createFromWkt.
  • if the above does not match perform a whole text search on proj4 string (if not null)
  • if none of the above match convert the proj4 string to an OGR CRS then check if its a geocs or a proj cs (using ogr isGeographic) then sequentially walk through the database (first users qgis.db srs tbl then system srs.db tbl), converting each entry into an ogr srs and using isSame or isSameGeocs (essentially calling the == overloaded operator). We'll try to be smart about this and first parse out the proj and ellpse strings and only check for a match in entities that have the same ellps and proj entries so that it doesn't munch yer cpu so much.
Parameters
theProjStringA proj4 format string
Returns
bool TRUE if success else false
bool QgsCoordinateReferenceSystem::createFromSrid ( const long  theSrid)

Set up this srs by fetching the appropriate information from the sqlite backend. First the system level read only srs.db will be checked and then the users ~/.qgis/qgis.db database will be checked for a match.

Note
Any members will be overwritten during this process.
Parameters
theSridThe postgis SRID for the desired spatial reference system.
bool QgsCoordinateReferenceSystem::createFromSrsId ( const long  theSrsId)

Set up this srs by fetching the appropriate information from the sqlite backend. If the srsid is < 100000, only the system srs.db will be checked. If the srsid > 100000 the srs will be retrieved from the ~/.qgis/qgis.db

Note
Any members will be overwritten during this process.
Parameters
theSrsIdThe QGIS SrsId for the desired spatial reference system.
Returns
bool TRUE if success else false
bool QgsCoordinateReferenceSystem::createFromString ( const QString &  theDefinition)

Set up this srs from a string definition, by default a WKT definition. Otherwise the string defines a authority, followed by a colon, followed by the definition. The authority can be one of "epsg", "postgis", "internal" for integer definitions, and "wkt" or "proj4" for string definitions. The implementation of each authority uses the corresponding createFrom... function.

Parameters
theDefinitionA String containing a coordinate reference system definition.
bool QgsCoordinateReferenceSystem::createFromUserInput ( const QString &  theDefinition)

Set up this srs from a 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.4 string, filename (with WKT, XML or PROJ.4 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 )
  @note this function generates a WKT string using OSRSetFromUserInput() and
  passes it to createFromWkt() function.
  @param theDefinition A String containing a coordinate reference system definition.

  @note added in 1.8
bool QgsCoordinateReferenceSystem::createFromWkt ( const QString &  theWkt)

Set up this srs using a Wkt spatial ref sys definition. The wkt will be converted to a proj4 string using OGR helper functions. After this the srs databasses will be searched for matches. First the system level read only srs.db will be checked and then the users ~/.qgis/qgis.db database will be checked for a match.

Note
Any members will be overwritten during this process.
SRID and EpsgCrsId may be blank if no match can be found on srs db.
Parameters
theWktThe Wkt for the desired spatial reference system.
Returns
bool TRUE if success else false
CUSTOM_CRS_VALIDATION QgsCoordinateReferenceSystem::customSrsValidation ( )
static

Gets custom function.

Note
not available in python bindings
QString QgsCoordinateReferenceSystem::description ( ) const

Get the Description

Returns
QString the Description A textual description of the srs.
Note
A zero length string will be returned if the description is uninitialised
QString QgsCoordinateReferenceSystem::ellipsoidAcronym ( ) const

Get the Ellipsoid Acronym

Returns
QString theEllipsoidAcronym The official proj4 acronym for the ellipoid
Note
A zero length string will be returned if the ellipsoidAcronym is uninitialised
long QgsCoordinateReferenceSystem::findMatchingProj ( )

This is a globbing function to try to find a record in the database that matches a CRS defined only by a proj4string. The goal is to learn what the tbl_srs.srs_id value is for the CRS. Internally the source CRS is converted to an OGR srs object using the proj4string call and then every record in the database that matches projection and ellipsoid will be converted to an OGR srs in turn and compared to the source CRS. There are some gotchas with using ogr isSame() srs comparison, but its more effective than using straight string comparison of proj4params.

Note
The ellipsoid and projection acronyms must be set as well as the proj4string!
Returns
long the SrsId of the matched CRS
QString QgsCoordinateReferenceSystem::geographicCRSAuthId ( ) const

Returns auth id of related geographic CRS.

bool QgsCoordinateReferenceSystem::geographicFlag ( ) const

Get this Geographic? flag

Returns
bool theGeoFlag Whether this is a geographic or projected coordinate system
bool QgsCoordinateReferenceSystem::isValid ( ) const

Find out whether this CRS is correctly initialised and usable

QGis::UnitType QgsCoordinateReferenceSystem::mapUnits ( ) const

Get the units that the projection is in

Returns
QGis::UnitType that gives the units for the coordinate system
bool QgsCoordinateReferenceSystem::operator!= ( const QgsCoordinateReferenceSystem theSrs) const

Overloaded != operator used to compare to CRS's. Returns opposite bool value to operator ==

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

Assignment operator.

bool QgsCoordinateReferenceSystem::operator== ( const QgsCoordinateReferenceSystem theSrs) const

Overloaded == operator used to compare to CRS's. Internally it will delegate to the equals method described below

long QgsCoordinateReferenceSystem::postgisSrid ( ) const

Get the postgis srid for this srs

Returns
long theSRID the Postgis spatial_ref_sys identifier for this srs (defaults to 0)
QString QgsCoordinateReferenceSystem::projectionAcronym ( ) const

Get the Projection Acronym

Returns
QString theProjectionAcronym The official proj4 acronym for the projection family
Note
A zero length string will be returned if the projectionAcronym is uninitialised
bool QgsCoordinateReferenceSystem::readXML ( QDomNode &  theNode)

Restores state from the given Dom node.

Parameters
theNodeThe node from which state will be restored
Returns
bool True on success, False on failure
bool QgsCoordinateReferenceSystem::saveAsUserCRS ( QString  name)

Copied from QgsCustomProjectionDialog /// Please refactor into SQL handler !!! ///.

Save the proj4-string as a custom CRS

Returns
bool true if success else false
void QgsCoordinateReferenceSystem::setCustomSrsValidation ( CUSTOM_CRS_VALIDATION  f)
static

Sets custom function to force valid CRS QGIS uses implementation in QgisGui::customSrsValidation.

Note
not available in python bindings
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() .
added in 1.8
void QgsCoordinateReferenceSystem::setValidationHint ( QString  html)

Set user hint for validation

long QgsCoordinateReferenceSystem::srsid ( ) const

Get the SrsId - if possible

Returns
long theSrsId The internal sqlite3 srs.db primary key for this srs
int QgsCoordinateReferenceSystem::syncDb ( )
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
added in 1.8
QString QgsCoordinateReferenceSystem::toProj4 ( ) const

Get the Proj Proj4 string representation of this srs.

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
QString theProj4String Proj4 format specifies that define this srs.
Note
A zero length string will be returned if the toProj4 is uninitialised
QString QgsCoordinateReferenceSystem::toWkt ( ) const

A helper to get an wkt representation of this srs

Returns
string containing Wkt of the srs
void QgsCoordinateReferenceSystem::validate ( )

Perform some validation on this CRS. If the sts doesn't validate the default behaviour 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 srs to be valid.
QString QgsCoordinateReferenceSystem::validationHint ( )

Get user hint for validation

bool QgsCoordinateReferenceSystem::writeXML ( QDomNode &  theNode,
QDomDocument &  theDoc 
) const

Stores state to the given Dom node in the given document. Below is an example of the generated tag.

     <spatialrefsys>
         <proj4>+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs </proj4>
          <srsid>2585</srsid>
          <srid>4326</srid>
          <epsg>4326</epsg>
          <description>WGS 84</description>
          <projectionacronym>longlat</projectionacronym>
          <ellipsoidacronym>WGS84</ellipsoidacronym>
      </spatialrefsys>
Parameters
theNodeThe node in which state will be restored
theDocThe document in which state will be stored
Returns
bool True on success, False on failure

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