QgsCoordinateTransform::transformCoords(): with PROJ 6, do no raise o…

…n partial failure of multiple point transformation Fixes #32973 or at least improve it significantly Currently with PROJ 6 transformCoords() will raise an exception as soon as a single point fails to transform. With PROJ < 6, this (generally) did not occur. Exceptions were raised only (mostly) on failures on single point. Imitate that
qgis · Nov 23, 2019 · ed7d13d · ed7d13d
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diff --git a/src/core/qgscoordinatetransform.cpp b/src/core/qgscoordinatetransform.cpp
@@ -662,7 +662,18 @@ void QgsCoordinateTransform::transformCoords( int numPoints, double *x, double *
                       y, sizeof( double ), numPoints,
                       z, sizeof( double ), numPoints,
                       nullptr, sizeof( double ), 0 );
-  projResult = proj_errno( projData );
+  // Try to - approximatively - emulate the behavior of pj_transform()...
+  // In the case of a single point transform, and a transformation error occurs,
+  // pj_transform() would return the errno. In cases of multiple point transform,
+  // it would continue (for non-transient errors, that is pipeline definition
+  // errors) and just set the resulting x,y to infinity. This is in fact a
+  // bit more subtle than that, and I'm not completely sure the logic in
+  // pj_transform() was really sane & fully bullet proof
+  // So here just check proj_errno() for single point transform
+  if ( numPoints == 1 )
+  {
+    projResult = proj_errno( projData );
+  }
 #else
   bool sourceIsLatLong = false;
   bool destIsLatLong = false;

diff --git a/tests/src/core/testqgscoordinatetransform.cpp b/tests/src/core/testqgscoordinatetransform.cpp
@@ -42,6 +42,8 @@ class TestQgsCoordinateTransform: public QObject
     void transform();
     void transformLKS();
     void transformContextNormalize();
+    void transformErrorMultiplePoints();
+    void transformErrorOnePoint();
 };
 
 
@@ -493,5 +495,42 @@ void TestQgsCoordinateTransform::transformContextNormalize()
 #endif
 }
 
+
+void TestQgsCoordinateTransform::transformErrorMultiplePoints()
+{
+  // Check that we don't throw an exception when transforming multiple
+  // points and at least one fails.
+  QgsCoordinateTransformContext context;
+  QgsCoordinateTransform ct( QgsCoordinateReferenceSystem::fromEpsgId( 4326 ), QgsCoordinateReferenceSystem::fromEpsgId( 3857 ), context );
+  QVERIFY( ct.isValid() );
+  double x[] = { 0, -1000 };
+  double y[] = { 0, 0 };
+  double z[] = { 0, 0 };
+  ct.transformCoords( 2, x, y, z );
+  QGSCOMPARENEAR( x[0], 0, 0.01 );
+  QGSCOMPARENEAR( y[0], 0, 0.01 );
+  QVERIFY( !std::isfinite( x[1] ) );
+  QVERIFY( !std::isfinite( y[1] ) );
+}
+
+
+void TestQgsCoordinateTransform::transformErrorOnePoint()
+{
+  QgsCoordinateTransformContext context;
+  QgsCoordinateTransform ct( QgsCoordinateReferenceSystem::fromEpsgId( 4326 ), QgsCoordinateReferenceSystem::fromEpsgId( 3857 ), context );
+  QVERIFY( ct.isValid() );
+  double x[] = {  -1000 };
+  double y[] = {  0 };
+  double z[] = {  0 };
+  try
+  {
+    ct.transformCoords( 1, x, y, z );
+    QVERIFY( false );
+  }
+  catch ( QgsCsException & )
+  {
+  }
+}
+
 QGSTEST_MAIN( TestQgsCoordinateTransform )
 #include "testqgscoordinatetransform.moc"