Don't try to use a fallback transform when we've already established

that only a single transform is possible between a CRS pair (since we've already tried that transform, it's pointless to re-try it and expect different results) Avoids superious "fallback transform used" warnings when only one operation is possible between a CRS pair
qgis · Feb 21, 2020 · 1c8aacf · 1c8aacf
1 parent 5f2660a
commit 1c8aacf
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Showing 3 changed files with 14 additions and 5 deletions.
diff --git a/src/core/qgscoordinatetransform.cpp b/src/core/qgscoordinatetransform.cpp
@@ -743,7 +743,9 @@ void QgsCoordinateTransform::transformCoords( int numPoints, double *x, double *
 #if PROJ_VERSION_MAJOR>=6
 
   mFallbackOperationOccurred = false;
-  if ( actualRes != 0 && ( d->mAllowFallbackTransforms || mBallparkTransformsAreAppropriate ) )
+  if ( actualRes != 0
+       && ( d->mAvailableOpCount > 1 || d->mAvailableOpCount == -1 ) // only use fallbacks if more than one operation is possible -- otherwise we've already tried it and it failed
+       && ( d->mAllowFallbackTransforms || mBallparkTransformsAreAppropriate ) )
   {
     // fail #1 -- try with getting proj to auto-pick an appropriate coordinate operation for the points
     if ( PJ *transform = d->threadLocalFallbackProjData() )

diff --git a/src/core/qgscoordinatetransform_p.cpp b/src/core/qgscoordinatetransform_p.cpp
@@ -99,6 +99,9 @@ QgsCoordinateTransformPrivate::QgsCoordinateTransformPrivate( const QgsCoordinat
 
 QgsCoordinateTransformPrivate::QgsCoordinateTransformPrivate( const QgsCoordinateTransformPrivate &other )
   : QSharedData( other )
+#if PROJ_VERSION_MAJOR >= 6
+  , mAvailableOpCount( other.mAvailableOpCount )
+#endif
   , mIsValid( other.mIsValid )
   , mShortCircuit( other.mShortCircuit )
   , mSourceCRS( other.mSourceCRS )
@@ -139,6 +142,9 @@ void QgsCoordinateTransformPrivate::invalidate()
 {
   mShortCircuit = true;
   mIsValid = false;
+#if PROJ_VERSION_MAJOR >= 6
+  mAvailableOpCount = -1;
+#endif
 }
 
 bool QgsCoordinateTransformPrivate::initialize()
@@ -387,8 +393,8 @@ ProjData QgsCoordinateTransformPrivate::threadLocalProjData()
 
     if ( PJ_OBJ_LIST *ops = proj_create_operations( context, mSourceCRS.projObject(), mDestCRS.projObject(), operationContext ) )
     {
-      int count = proj_list_get_count( ops );
-      if ( count < 1 )
+      mAvailableOpCount = proj_list_get_count( ops );
+      if ( mAvailableOpCount < 1 )
       {
         // huh?
         int errNo = proj_context_errno( context );
@@ -401,7 +407,7 @@ ProjData QgsCoordinateTransformPrivate::threadLocalProjData()
           nonAvailableError = QObject::tr( "No coordinate operations are available between these two reference systems" );
         }
       }
-      else if ( count == 1 )
+      else if ( mAvailableOpCount == 1 )
       {
         // only a single operation available. Can we use it?
         transform.reset( proj_list_get( context, ops, 0 ) );
@@ -466,7 +472,7 @@ ProjData QgsCoordinateTransformPrivate::threadLocalProjData()
         QgsDatumTransform::TransformDetails preferred;
         bool missingPreferred = false;
         bool stillLookingForPreferred = true;
-        for ( int i = 0; i < count; ++ i )
+        for ( int i = 0; i < mAvailableOpCount; ++ i )
         {
           transform.reset( proj_list_get( context, ops, i ) );
           const bool isInstantiable = transform && proj_coordoperation_is_instantiable( context, transform.get() );

diff --git a/src/core/qgscoordinatetransform_p.h b/src/core/qgscoordinatetransform_p.h
@@ -103,6 +103,7 @@ class QgsCoordinateTransformPrivate : public QSharedData
     ProjData threadLocalProjData();
 
 #if PROJ_VERSION_MAJOR>=6
+    int mAvailableOpCount = -1;
     ProjData threadLocalFallbackProjData();
 
     // Only meant to be called by QgsCoordinateTransform::removeFromCacheObjectsBelongingToCurrentThread()