Correctly handle inverse transforms with reversed axis CRS in proj 6.0 builds

This logic is too complex and fragile -- we should drop support for proj 6.0
as soon as we can, so that we can the inbuilt handling which
is enabled for proj >= 6.1 only.

Author: nyalldawson

src/core/qgscoordinatetransform.cpp

@@ -648,16 +648,16 @@ void QgsCoordinateTransform::transformCoords( int numPoints, double *x, double *
 
   int projResult = 0;
 #if PROJ_VERSION_MAJOR>=6
-  const bool sourceAxisOrderSwapped = d->mSourceAxisOrderSwapped;
-  const bool destinationAxisOrderSwapped = d->mDestAxisOrderSwapped;
+  const bool sourceAxisOrderSwapped =  direction == ForwardTransform ? d->mSourceAxisOrderSwapped : d->mDestAxisOrderSwapped;
 
   proj_trans_generic( projData, direction == ForwardTransform ? PJ_FWD : PJ_INV,
                       !sourceAxisOrderSwapped ? x : y, sizeof( double ), numPoints,
                       !sourceAxisOrderSwapped ? y : x, sizeof( double ), numPoints,
                       z, sizeof( double ), numPoints,
                       nullptr, sizeof( double ), 0 );
   projResult = proj_errno( projData );
-  if ( projResult == 0 && destinationAxisOrderSwapped )
+  // ewww - this logic is gross. We should drop support for PROJ 6.0 as quickly as possible and dump this code (in favour of built in methods used for >=6.1 builds)
+  if ( projResult == 0 && ( d->mSourceAxisOrderSwapped != d->mDestAxisOrderSwapped ) )
   {
     size_t size = sizeof( double ) * numPoints;
     void *tmp = malloc( size );

tests/src/core/testqgscoordinatetransform.cpp

@@ -260,18 +260,27 @@ void TestQgsCoordinateTransform::transform_data()
   QTest::addColumn<QgsCoordinateReferenceSystem>( "destCrs" );
   QTest::addColumn<double>( "x" );
   QTest::addColumn<double>( "y" );
+  QTest::addColumn<int>( "direction" );
   QTest::addColumn<double>( "outX" );
   QTest::addColumn<double>( "outY" );
   QTest::addColumn<double>( "precision" );
 
   QTest::newRow( "To geographic" )
       << QgsCoordinateReferenceSystem::fromEpsgId( 3111 )
       << QgsCoordinateReferenceSystem::fromEpsgId( 4326 )
-      << 2545059.0 << 2393190.0 << 145.512750 << -37.961375 << 0.000001;
+      << 2545059.0 << 2393190.0 << static_cast< int >( QgsCoordinateTransform::ForwardTransform ) << 145.512750 << -37.961375 << 0.000001;
   QTest::newRow( "From geographic" )
       << QgsCoordinateReferenceSystem::fromEpsgId( 4326 )
       << QgsCoordinateReferenceSystem::fromEpsgId( 3111 )
-      << 145.512750 <<  -37.961375 << 2545059.0 << 2393190.0 << 0.1;
+      << 145.512750 <<  -37.961375 << static_cast< int >( QgsCoordinateTransform::ForwardTransform ) << 2545059.0 << 2393190.0 << 0.1;
+  QTest::newRow( "To geographic (reverse)" )
+      << QgsCoordinateReferenceSystem::fromEpsgId( 3111 )
+      << QgsCoordinateReferenceSystem::fromEpsgId( 4326 )
+      << 145.512750 <<  -37.961375 << static_cast< int >( QgsCoordinateTransform::ReverseTransform ) << 2545059.0 << 2393190.0 << 0.1;
+  QTest::newRow( "From geographic (reverse)" )
+      << QgsCoordinateReferenceSystem::fromEpsgId( 4326 )
+      << QgsCoordinateReferenceSystem::fromEpsgId( 3111 )
+      << 2545058.9675128171 << 2393190.0509782173 << static_cast< int >( QgsCoordinateTransform::ReverseTransform ) << 145.512750 << -37.961375 << 0.000001;
 }
 
 void TestQgsCoordinateTransform::transform()
@@ -280,14 +289,15 @@ void TestQgsCoordinateTransform::transform()
   QFETCH( QgsCoordinateReferenceSystem, destCrs );
   QFETCH( double, x );
   QFETCH( double, y );
+  QFETCH( int, direction );
   QFETCH( double, outX );
   QFETCH( double, outY );
   QFETCH( double, precision );
 
   double z = 0;
   QgsCoordinateTransform ct( sourceCrs, destCrs, QgsProject::instance() );
 
-  ct.transformInPlace( x, y, z );
+  ct.transformInPlace( x, y, z, static_cast<  QgsCoordinateTransform::TransformDirection >( direction ) );
   QGSCOMPARENEAR( x, outX, precision );
   QGSCOMPARENEAR( y, outY, precision );
 }