From 5b17456393a6dc6407074a4879e5905e42ed3e37 Mon Sep 17 00:00:00 2001
From: Alvaro Huarte <ahuarte47@yahoo.es>
Date: Thu, 30 Jun 2016 12:20:29 +0200
Subject: [PATCH 1/2] Fix zoom and scale of MapCanvas when DestinationCrs
 changes

---
 src/gui/qgsmapcanvas.cpp | 40 +++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 19 deletions(-)

diff --git a/src/gui/qgsmapcanvas.cpp b/src/gui/qgsmapcanvas.cpp
index dc5e6e18599..daa5cba4f39 100644
--- a/src/gui/qgsmapcanvas.cpp
+++ b/src/gui/qgsmapcanvas.cpp
@@ -558,32 +558,34 @@ void QgsMapCanvas::setDestinationCrs( const QgsCoordinateReferenceSystem &crs )
   if ( mSettings.destinationCrs() == crs )
     return;
 
-  if ( mSettings.hasCrsTransformEnabled() )
+  // try to reproject current extent to the new one
+  QgsRectangle rect;
+  if ( !mSettings.visibleExtent().isEmpty() )
   {
-    // try to reproject current extent to the new one
-    QgsRectangle rect;
-    if ( !mSettings.visibleExtent().isEmpty() )
+    QgsCoordinateTransform transform( mSettings.destinationCrs(), crs );
+    try
     {
-      QgsCoordinateTransform transform( mSettings.destinationCrs(), crs );
-      try
-      {
-        rect = transform.transformBoundingBox( mSettings.visibleExtent() );
-      }
-      catch ( QgsCsException &e )
-      {
-        Q_UNUSED( e );
-        QgsDebugMsg( QString( "Transform error caught: %1" ).arg( e.what() ) );
-      }
+      rect = transform.transformBoundingBox( mSettings.visibleExtent() );
     }
-    if ( !rect.isEmpty() )
+    catch ( QgsCsException &e )
     {
-      setExtent( rect );
+      Q_UNUSED( e );
+      QgsDebugMsg( QString( "Transform error caught: %1" ).arg( e.what() ) );
     }
-
-    QgsDebugMsg( "refreshing after destination CRS changed" );
-    refresh();
   }
 
+  if ( !mSettings.hasCrsTransformEnabled() )
+  {
+    mSettings.setMapUnits( crs.mapUnits() );
+  }
+  if ( !rect.isEmpty() )
+  {
+    setExtent( rect );
+  }
+
+  QgsDebugMsg( "refreshing after destination CRS changed" );
+  refresh();
+
   mSettings.setDestinationCrs( crs );
 
   updateDatumTransformEntries();

From 4057c3a6b49dd409348a2345d43011a8239a4f86 Mon Sep 17 00:00:00 2001
From: Alvaro Huarte <ahuarte47@yahoo.es>
Date: Fri, 1 Jul 2016 11:05:01 +0200
Subject: [PATCH 2/2] Add test code

---
 src/core/qgstestutils.h                | 11 +++++++++++
 tests/src/gui/testprojectionissues.cpp | 25 +++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/src/core/qgstestutils.h b/src/core/qgstestutils.h
index 8561b7a109c..12c52f76ee6 100644
--- a/src/core/qgstestutils.h
+++ b/src/core/qgstestutils.h
@@ -32,5 +32,16 @@
     QVERIFY( qgsDoubleNear( value, expected, epsilon ) ); \
   }
 
+#define QGSCOMPARENEARPOINT(point1,point2,epsilon) { \
+    QGSCOMPARENEAR( point1.x(), point2.x(), epsilon ); \
+    QGSCOMPARENEAR( point1.y(), point2.y(), epsilon ); \
+  }
+
+#define QGSCOMPARENEARRECTANGLE(rectangle1,rectangle2,epsilon) { \
+    QGSCOMPARENEAR( rectangle1.xMinimum(), rectangle2.xMinimum(), epsilon ); \
+    QGSCOMPARENEAR( rectangle1.xMaximum(), rectangle2.xMaximum(), epsilon ); \
+    QGSCOMPARENEAR( rectangle1.yMinimum(), rectangle2.yMinimum(), epsilon ); \
+    QGSCOMPARENEAR( rectangle1.yMaximum(), rectangle2.yMaximum(), epsilon ); \
+  }
 
 #endif // QGSTESTUTILS_H
diff --git a/tests/src/gui/testprojectionissues.cpp b/tests/src/gui/testprojectionissues.cpp
index 2f76121c444..b11f255ab69 100644
--- a/tests/src/gui/testprojectionissues.cpp
+++ b/tests/src/gui/testprojectionissues.cpp
@@ -23,6 +23,7 @@
 #include "qgsrasterlayer.h"
 #include <QObject>
 #include <QtTest/QtTest>
+#include "qgstestutils.h"
 
 class TestProjectionIssues : public QObject
 {
@@ -39,6 +40,7 @@ class TestProjectionIssues : public QObject
     void init();// will be called before each testfunction is executed.
     void cleanup();// will be called after every testfunction.
     void issue5895();// test for #5895
+    void issue15183();// test for #15183
 
   private:
     QgsRasterLayer* mRasterLayer;
@@ -109,5 +111,28 @@ void TestProjectionIssues::issue5895()
   mMapCanvas->zoomByFactor( 2.0 ); // Zoom out. This should exceed the transform limits.
 }
 
+void TestProjectionIssues::issue15183()
+{
+  QgsRectangle largeExtent( -610861, 5101721, 2523921, 6795055 );
+  mMapCanvas->setExtent( largeExtent );
+
+  // Set to CRS's
+  QgsCoordinateReferenceSystem sourceCRS;
+  sourceCRS = mMapCanvas->mapSettings().destinationCrs();
+  QgsCoordinateReferenceSystem targetCRS;
+  targetCRS.createFromId( 4326, QgsCoordinateReferenceSystem::EpsgCrsId );
+
+  QgsCoordinateTransform ct( sourceCRS, targetCRS );
+  QgsRectangle initialExtent = ct.transformBoundingBox( mMapCanvas->extent() );
+
+  mMapCanvas->setCrsTransformEnabled( false );
+  mMapCanvas->setDestinationCrs( targetCRS );
+
+  QgsRectangle currentExtent = mMapCanvas->extent();
+
+  // Compare center
+  QGSCOMPARENEARPOINT( initialExtent.center(), currentExtent.center(), 0.00001 );
+}
+
 QTEST_MAIN( TestProjectionIssues )
 #include "testprojectionissues.moc"