Fix working of Helmert transform between the horizontal part of 2 compoundCRS (fixes #2108)

2 files changed, 46 insertions, 0 deletions

diff --git a/src/iso19111/coordinateoperation.cpp b/src/iso19111/coordinateoperation.cpp
index 91801100..1b35e35a 100644
--- a/src/iso19111/coordinateoperation.cpp
+++ b/src/iso19111/coordinateoperation.cpp
@@ -8824,6 +8824,16 @@ static void setupPROJGeodeticSourceCRS(io::PROJStringFormatter *formatter,
                                        const crs::CRSNNPtr &crs, bool addPushV3,
                                        const char *trfrm_name) {
     auto sourceCRSGeog = dynamic_cast<const crs::GeographicCRS *>(crs.get());
+    if (!sourceCRSGeog) {
+        auto compoundCRS = dynamic_cast<const crs::CompoundCRS *>(crs.get());
+        if (compoundCRS) {
+            const auto &components = compoundCRS->componentReferenceSystems();
+            if (!components.empty()) {
+                sourceCRSGeog = dynamic_cast<const crs::GeographicCRS *>(
+                    components[0].get());
+            }
+        }
+    }
     if (sourceCRSGeog) {
         formatter->startInversion();
         sourceCRSGeog->_exportToPROJString(formatter);
@@ -8852,6 +8862,16 @@ static void setupPROJGeodeticTargetCRS(io::PROJStringFormatter *formatter,
                                        const crs::CRSNNPtr &crs, bool addPopV3,
                                        const char *trfrm_name) {
     auto targetCRSGeog = dynamic_cast<const crs::GeographicCRS *>(crs.get());
+    if (!targetCRSGeog) {
+        auto compoundCRS = dynamic_cast<const crs::CompoundCRS *>(crs.get());
+        if (compoundCRS) {
+            const auto &components = compoundCRS->componentReferenceSystems();
+            if (!components.empty()) {
+                targetCRSGeog = dynamic_cast<const crs::GeographicCRS *>(
+                    components[0].get());
+            }
+        }
+    }
     if (targetCRSGeog) {
         formatter->addStep("cart");
         formatter->setCurrentStepInverted(true);
diff --git a/test/unit/test_operation.cpp b/test/unit/test_operation.cpp
index 5bea9099..924ad950 100644
--- a/test/unit/test_operation.cpp
+++ b/test/unit/test_operation.cpp
@@ -7231,6 +7231,32 @@ TEST(operation, compoundCRS_to_compoundCRS_context) {
 
 // ---------------------------------------------------------------------------
 
+TEST(operation, compoundCRS_to_compoundCRS_context_helmert_noop) {
+    auto dbContext = DatabaseContext::create();
+    auto authFactory = AuthorityFactory::create(dbContext, "EPSG");
+    auto ctxt = CoordinateOperationContext::create(authFactory, nullptr, 0.0);
+    ctxt->setGridAvailabilityUse(
+        CoordinateOperationContext::GridAvailabilityUse::
+            IGNORE_GRID_AVAILABILITY);
+    ctxt->setSpatialCriterion(
+        CoordinateOperationContext::SpatialCriterion::PARTIAL_INTERSECTION);
+    // WGS84 + EGM96
+    auto objSrc = createFromUserInput("EPSG:4326+3855", dbContext);
+    auto srcCrs = nn_dynamic_pointer_cast<CompoundCRS>(objSrc);
+    ASSERT_TRUE(srcCrs != nullptr);
+    // ETRS89 + EGM96
+    auto objDest = createFromUserInput("EPSG:4258+3855", dbContext);
+    auto destCrs = nn_dynamic_pointer_cast<CompoundCRS>(objDest);
+    ASSERT_TRUE(destCrs != nullptr);
+    auto list = CoordinateOperationFactory::create()->createOperations(
+        NN_NO_CHECK(srcCrs), NN_NO_CHECK(destCrs), ctxt);
+    ASSERT_GE(list.size(), 1U);
+    EXPECT_EQ(list[0]->exportToPROJString(PROJStringFormatter::create().get()),
+              "+proj=noop");
+}
+
+// ---------------------------------------------------------------------------
+
 TEST(operation, vertCRS_to_vertCRS) {
 
     auto vertcrs_m_obj = PROJStringParser().createFromPROJString("+vunits=m");