From d1fa64ff3eeb515431bc7fe4d2d3beae4071051a Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Thu, 28 Nov 2024 21:58:34 +0100
Subject: [PATCH] proj_trans_bounds(): make it work when target CRS is a
 CompoundCRS

---
 src/4D_api.cpp           | 14 ++++++++++++--
 test/unit/test_c_api.cpp | 21 +++++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/4D_api.cpp b/src/4D_api.cpp
index 478dab8fa8..99e56ffda2 100644
--- a/src/4D_api.cpp
+++ b/src/4D_api.cpp
@@ -1416,8 +1416,18 @@ static int target_crs_lon_lat_order(PJ_CONTEXT *transformer_ctx,
                                "Unable to retrieve target CRS");
         return -1;
     }
-    PJ *coord_system_pj =
-        proj_crs_get_coordinate_system(transformer_ctx, target_crs);
+    PJ *coord_system_pj;
+    if (proj_get_type(target_crs) == PJ_TYPE_COMPOUND_CRS) {
+        PJ *horiz_crs = proj_crs_get_sub_crs(transformer_ctx, target_crs, 0);
+        if (!horiz_crs)
+            return -1;
+        coord_system_pj =
+            proj_crs_get_coordinate_system(transformer_ctx, horiz_crs);
+        proj_destroy(horiz_crs);
+    } else {
+        coord_system_pj =
+            proj_crs_get_coordinate_system(transformer_ctx, target_crs);
+    }
     proj_destroy(target_crs);
     if (coord_system_pj == nullptr) {
         proj_context_log_debug(transformer_ctx,
diff --git a/test/unit/test_c_api.cpp b/test/unit/test_c_api.cpp
index 4a6450979a..ff6d13dab1 100644
--- a/test/unit/test_c_api.cpp
+++ b/test/unit/test_c_api.cpp
@@ -6515,6 +6515,27 @@ TEST_F(CApi, proj_trans_bounds__south_pole) {
 
 // ---------------------------------------------------------------------------
 
+TEST_F(CApi, proj_trans_bounds_to_compound_crs) {
+    // EPSG:9707 = "WGS 84 + EGM96 height"
+    auto P = proj_create_crs_to_crs(m_ctxt, "EPSG:4326", "EPSG:9707", nullptr);
+    ObjectKeeper keeper_P(P);
+    ASSERT_NE(P, nullptr);
+    double out_left;
+    double out_bottom;
+    double out_right;
+    double out_top;
+    int success =
+        proj_trans_bounds(m_ctxt, P, PJ_FWD, 40, -120, 64, -80, &out_left,
+                          &out_bottom, &out_right, &out_top, 0);
+    EXPECT_TRUE(success == 1);
+    EXPECT_NEAR(out_left, 40, 1e-8);
+    EXPECT_NEAR(out_bottom, -120, 1e-8);
+    EXPECT_NEAR(out_right, 64, 1e-8);
+    EXPECT_NEAR(out_top, -80, 1e-8);
+}
+
+// ---------------------------------------------------------------------------
+
 TEST_F(CApi, proj_crs_has_point_motion_operation) {
     auto ctxt = proj_create_operation_factory_context(m_ctxt, nullptr);
     ASSERT_NE(ctxt, nullptr);