Use QgsCRSCache instead of looking up CRS by srs id (refs #15193)

Author: nyalldawson

python/core/qgscoordinatereferencesystem.sip

@@ -77,6 +77,7 @@ class QgsCoordinateReferenceSystem
      * @note Any members will be overwritten during this process.
      * @param theSrsId The QGIS SrsId for the desired spatial reference system.
      * @return bool TRUE if success else false
+     * @note this method is expensive. Consider using QgsCRSCache::crsBySrsId() instead.
      */
     bool createFromSrsId( const long theSrsId );
 

python/core/qgscrscache.sip

@@ -71,6 +71,14 @@ class QgsCRSCache
     */
     QgsCoordinateReferenceSystem crsByProj4( const QString& proj4 ) const;
 
+    /** Returns the CRS from a specified QGIS SRS ID.
+     * @param srsId internal QGIS SRS ID
+     * @returns matching CRS, or an invalid CRS if ID could not be found
+     * @note added in QGIS 2.16
+     * @see QgsCoordinateReferenceSystem::createFromSrsId()
+    */
+    QgsCoordinateReferenceSystem crsBySrsId( long srsId ) const;
+
     /** Updates the cached definition of a CRS. Should be called if the definition of a user-created
      * CRS has been changed.
      * @param authid CRS auth ID, eg "EPSG:4326" or "USER:100009"

src/core/qgscoordinatereferencesystem.h

@@ -124,6 +124,7 @@ class CORE_EXPORT QgsCoordinateReferenceSystem
      * @note Any members will be overwritten during this process.
      * @param theSrsId The QGIS SrsId for the desired spatial reference system.
      * @return bool TRUE if success else false
+     * @note this method is expensive. Consider using QgsCRSCache::crsBySrsId() instead.
      */
     bool createFromSrsId( const long theSrsId );
 

src/core/qgscoordinatetransform.cpp

@@ -152,7 +152,7 @@ void QgsCoordinateTransform::setDestCRS( const QgsCoordinateReferenceSystem& the
 void QgsCoordinateTransform::setDestCRSID( long theCRSID )
 {
   //!todo Add some logic here to determine if the srsid is a system or user one
-  mDestCRS.createFromSrsId( theCRSID );
+  mDestCRS = QgsCRSCache::instance()->crsBySrsId( theCRSID );
   initialise();
 }
 

src/core/qgscrscache.cpp

@@ -143,7 +143,7 @@ QgsCoordinateReferenceSystem QgsCRSCache::crsByEpsgId( long epsg ) const
 
 QgsCoordinateReferenceSystem QgsCRSCache::crsByProj4( const QString& proj4 ) const
 {
-  QHash< QString, QgsCoordinateReferenceSystem >::const_iterator crsIt = mCRSProj4.find( proj4 );
+  QHash< QString, QgsCoordinateReferenceSystem >::const_iterator crsIt = mCRSProj4.constFind( proj4 );
   if ( crsIt == mCRSProj4.constEnd() )
   {
     QgsCoordinateReferenceSystem s;
@@ -158,3 +158,21 @@ QgsCoordinateReferenceSystem QgsCRSCache::crsByProj4( const QString& proj4 ) con
     return crsIt.value();
   }
 }
+
+QgsCoordinateReferenceSystem QgsCRSCache::crsBySrsId( long srsId ) const
+{
+  QHash< long, QgsCoordinateReferenceSystem >::const_iterator crsIt = mCRSSrsId.constFind( srsId );
+  if ( crsIt == mCRSSrsId.constEnd() )
+  {
+    QgsCoordinateReferenceSystem s;
+    if ( ! s.createFromSrsId( srsId ) )
+    {
+      return mCRSSrsId.insert( srsId, mInvalidCRS ).value();
+    }
+    return mCRSSrsId.insert( srsId, s ).value();
+  }
+  else
+  {
+    return crsIt.value();
+  }
+}

src/core/qgscrscache.h

@@ -97,6 +97,14 @@ class CORE_EXPORT QgsCRSCache
     */
     QgsCoordinateReferenceSystem crsByProj4( const QString& proj4 ) const;
 
+    /** Returns the CRS from a specified QGIS SRS ID.
+     * @param srsId internal QGIS SRS ID
+     * @returns matching CRS, or an invalid CRS if ID could not be found
+     * @note added in QGIS 2.16
+     * @see QgsCoordinateReferenceSystem::createFromSrsId()
+    */
+    QgsCoordinateReferenceSystem crsBySrsId( long srsId ) const;
+
     /** Updates the cached definition of a CRS. Should be called if the definition of a user-created
      * CRS has been changed.
      * @param authid CRS auth ID, eg "EPSG:4326" or "USER:100009"
@@ -110,6 +118,7 @@ class CORE_EXPORT QgsCRSCache
 
     mutable QHash< QString, QgsCoordinateReferenceSystem > mCRS;
     mutable QHash< QString, QgsCoordinateReferenceSystem > mCRSProj4;
+    mutable QHash< long, QgsCoordinateReferenceSystem > mCRSSrsId;
 
     /** CRS that is not initialized (returned in case of error)*/
     QgsCoordinateReferenceSystem mInvalidCRS;

src/core/qgsdistancearea.cpp

@@ -106,8 +106,7 @@ bool QgsDistanceArea::willUseEllipsoid() const
 
 void QgsDistanceArea::setSourceCrs( long srsid )
 {
-  QgsCoordinateReferenceSystem srcCRS;
-  srcCRS.createFromSrsId( srsid );
+  QgsCoordinateReferenceSystem srcCRS = QgsCRSCache::instance()->crsBySrsId( srsid );
   mCoordTransform->setSourceCrs( srcCRS );
 }
 

src/gui/qgsprojectionselectionwidget.cpp

@@ -87,8 +87,7 @@ QgsCoordinateReferenceSystem QgsProjectionSelectionWidget::crs() const
     case QgsProjectionSelectionWidget::RecentCrs:
     {
       long srsid = mCrsComboBox->itemData( mCrsComboBox->currentIndex(), Qt::UserRole + 1 ).toLongLong();
-      QgsCoordinateReferenceSystem crs;
-      crs.createFromSrsId( srsid );
+      QgsCoordinateReferenceSystem crs = QgsCRSCache::instance()->crsBySrsId( srsid );
       return crs;
     }
   }
@@ -174,8 +173,7 @@ void QgsProjectionSelectionWidget::comboIndexChanged( int idx )
     case QgsProjectionSelectionWidget::RecentCrs:
     {
       long srsid = mCrsComboBox->itemData( idx, Qt::UserRole + 1 ).toLongLong();
-      QgsCoordinateReferenceSystem crs;
-      crs.createFromSrsId( srsid );
+      QgsCoordinateReferenceSystem crs = QgsCRSCache::instance()->crsBySrsId( srsid );
       emit crsChanged( crs );
       return;
     }
@@ -252,8 +250,7 @@ void QgsProjectionSelectionWidget::addRecentCrs()
     }
 
     i++;
-    QgsCoordinateReferenceSystem crs;
-    crs.createFromSrsId( srsid );
+    QgsCoordinateReferenceSystem crs = QgsCRSCache::instance()->crsBySrsId( srsid );
     if ( crs.isValid() )
     {
       mCrsComboBox->addItem( tr( "%1 - %2" ).arg( crs.authid(), crs.description() ), QgsProjectionSelectionWidget::RecentCrs );

tests/src/python/test_qgscrscache.py

@@ -89,5 +89,23 @@ def testcrsByProj4(self):
         crs = QgsCRSCache.instance().crsByProj4('asdasdasd')
         self.assertFalse(crs.isValid())
 
+    def testcrsBySrsId(self):
+        """ test retrieving CRS from cache using srs id """
+
+        crs = QgsCRSCache.instance().crsBySrsId(3452)
+        self.assertTrue(crs.isValid())
+        self.assertEqual(crs.authid(), 'EPSG:4326')
+        # a second time, so crs is fetched from cache
+        crs = QgsCRSCache.instance().crsBySrsId(3452)
+        self.assertTrue(crs.isValid())
+        self.assertEqual(crs.authid(), 'EPSG:4326')
+
+        # invalid
+        crs = QgsCRSCache.instance().crsBySrsId(-9999)
+        self.assertFalse(crs.isValid())
+        # a second time, so invalid crs is fetched from cache
+        crs = QgsCRSCache.instance().crsBySrsId(-9999)
+        self.assertFalse(crs.isValid())
+
 if __name__ == '__main__':
     unittest.main()