[wms] Don't require an explicit tileMatrixSet URI param for WMTS

When no explicit WMTS tileMatrixSet is specified, use the first
returned by the GetCapabilities request. This allows creation
of raster layers with no upfront knowledge of the available
tile matrix sets, and avoids the need for Python scripts to
manually retrieve and parse the GetCapabilities in advance in
order to determine available tile set IDs.

src/providers/wms/qgswmscapabilities.cpp

@@ -1868,6 +1868,8 @@ void QgsWmsCapabilities::parseWMTSContents( const QDomElement &element )
     }
 
     mTileMatrixSets.insert( set.identifier, set );
+    if ( mFirstTileMatrixSetId.isEmpty() )
+      mFirstTileMatrixSetId = set.identifier;
   }
 
   //

src/providers/wms/qgswmscapabilities.h

@@ -1051,6 +1051,12 @@ class QgsWmsCapabilities
      */
     QHash<QString, QgsWmtsTileMatrixSet> mTileMatrixSets;
 
+    /**
+     * ID of the first tile matrix returned in the capabilities, to be used as the default
+     * if no specific tile matrix is specified.
+     */
+    QString mFirstTileMatrixSetId;
+
     //temporarily caches invert axis setting for each crs
     QHash<QString, bool> mCrsInvertAxis;
 

src/providers/wms/qgswmsprovider.cpp

@@ -593,6 +593,22 @@ bool QgsWmsProvider::setImageCrs( QString const &crs )
     }
 
     mNativeResolutions.clear();
+
+    if ( mSettings.mTileMatrixSetId.isEmpty() && !mCaps.mFirstTileMatrixSetId.isEmpty() )
+    {
+      // if no explicit tile matrix set specified, use first listed
+      mSettings.mTileMatrixSetId = mCaps.mFirstTileMatrixSetId;
+      for ( int i = 0; i < mCaps.mTileLayersSupported.size(); i++ )
+      {
+        QgsWmtsTileLayer *tl = &mCaps.mTileLayersSupported[i];
+        if ( tl->identifier != mSettings.mActiveSubLayers[0] )
+          continue;
+
+        mTileLayer = tl;
+        break;
+      }
+    }
+
     if ( mCaps.mTileMatrixSets.contains( mSettings.mTileMatrixSetId ) )
     {
       mTileMatrixSet = &mCaps.mTileMatrixSets[ mSettings.mTileMatrixSetId ];

tests/src/providers/testqgswmsprovider.cpp

@@ -157,12 +157,21 @@ class TestQgsWmsProvider: public QgsTest
       // explicitly state crs and format
       {
         QgsWmsProvider provider( "contextualWMSLegend=0&crs=EPSG:4326&dpiMode=7&featureCount=10&format=image/jpg&layers=CountryGroup&styles=default&tileMatrixSet=standard&tilePixelRatio=0&url=http://localhost:8380/mapserv?xxx", QgsDataProvider::ProviderOptions(), &cap );
+        QCOMPARE( provider.mSettings.mTileMatrixSetId, QStringLiteral( "standard" ) );
         QCOMPARE( provider.crs().authid(), QStringLiteral( "EPSG:4326" ) );
         QCOMPARE( provider.mSettings.mImageMimeType, QStringLiteral( "image/jpg" ) );
       }
       // no crs or format specified, should use tile matrix crs
       {
         QgsWmsProvider provider( "contextualWMSLegend=0&dpiMode=7&featureCount=10&layers=CountryGroup&styles=default&tileMatrixSet=standard&tilePixelRatio=0&url=http://localhost:8380/mapserv?xxx", QgsDataProvider::ProviderOptions(), &cap );
+        QCOMPARE( provider.mSettings.mTileMatrixSetId, QStringLiteral( "standard" ) );
+        QCOMPARE( provider.crs().authid(), QStringLiteral( "EPSG:3857" ) );
+        QCOMPARE( provider.mSettings.mImageMimeType, QStringLiteral( "image/png" ) );
+      }
+      // no tileMatrixSet specified, should use first listed
+      {
+        QgsWmsProvider provider( "layers=CountryGroup&styles=default&tileDimensions=&url=http://localhost:8380/mapserv?xxx", QgsDataProvider::ProviderOptions(), &cap );
+        QCOMPARE( provider.mSettings.mTileMatrixSetId, QStringLiteral( "standard" ) );
         QCOMPARE( provider.crs().authid(), QStringLiteral( "EPSG:3857" ) );
         QCOMPARE( provider.mSettings.mImageMimeType, QStringLiteral( "image/png" ) );
       }