Transformation: no longer do vertical trasnformation when doing compound CRS to 2D CRS / add --3d to cs2cs

Previously, when computing transformation between a compound CRS and a
geographic/projected 2D CRS, the behaviour was similar to implicitly
promoting the 2D CRS to 3D CRS in the pipeline computation logic, hence
a geoid model could be applied. But note that when doing a geographic 3D
to geographic/projected 2D CRS transformation, we *did* not do this implicit
promotion and if a Helmert transformation existed between the datums, it
was done only in 2D. So this is a bit inconsistent and triggered the
comment in https://github.com/OSGeo/PROJ/issues/2318#issuecomment-1068924513

With this commit, we no longer do any vertical transformation when doing
compound CRS to the 2D CRS, but just take the transformation of the
horizontal part of the compound CRS to the 2D CRS.
Said otherwise, NAD83+NAVD88 to NAD83 will no longer lead to the
application of the geoid model. Unless you explicitly ask for the
promotion NAD83 to 3D.

Also related, in https://github.com/OSGeo/PROJ/issues/1563 that went to 6.3.0,
I changed cs2cs to automatically promote to 3D the CRS as soon as one of
them was compound, for the sake of being consistent with the past
behaviour. But it then becomes difficult to predict PROJ behaviour
depending on which level of it you consider...
This commit undoes that and adds an explicit --3d switch to cs2cs, similarly to
projinfo, to ask for promotion.

Other bug fix found in the process, when using legacy syntax, +init=epsg:4979,
(WGS 84 3D), the resulting CRS was 2D and not 3D.

6 files changed, 41 insertions, 22 deletions

diff --git a/test/cli/td_out.dist b/test/cli/td_out.dist
index 5c9b18d3..5957ebc3 100644
--- a/test/cli/td_out.dist
+++ b/test/cli/td_out.dist
@@ -35,5 +35,11 @@ NAD27 -> NAD83: 1st through ntv1 or ntv2, 2nd through conus
 55d00'00.000"N 111d00'00.000"W 0.0	55.0001	-111.0009 0.0000
 39d00'00.000"N 111d00'00.000"W 0.0	39.0000	-111.0007 0.0000
 ##############################################################
-WGS84 -> WGS84+EGM96
+WGS84 (2D) -> WGS84+EGM96
+2dE 49dN 0	2.00	49.00 0.00
+##############################################################
+WGS84 (3D) -> WGS84+EGM96
+2dE 49dN 0	2.00	49.00 -45.06
+##############################################################
+WGS84 (2D), promoted to 3D -> WGS84+EGM96
 2dE 49dN 0	2.00	49.00 -45.06
diff --git a/test/cli/testdatumfile b/test/cli/testdatumfile
index e974d34c..3496299f 100755
--- a/test/cli/testdatumfile
+++ b/test/cli/testdatumfile
@@ -124,12 +124,28 @@ EOF
 
 #
 echo "##############################################################" >> ${OUT}
-echo "WGS84 -> WGS84+EGM96" >> ${OUT}
+echo "WGS84 (2D) -> WGS84+EGM96" >> ${OUT}
 #
 $EXE +init=epsg:4326 +to +init=epsg:4326 +geoidgrids=egm96_15.gtx -E >>${OUT} <<EOF
 2dE 49dN 0
 EOF
 
+#
+echo "##############################################################" >> ${OUT}
+echo "WGS84 (3D) -> WGS84+EGM96" >> ${OUT}
+#
+$EXE +init=epsg:4979 +to +init=epsg:4326 +geoidgrids=egm96_15.gtx -E >>${OUT} <<EOF
+2dE 49dN 0
+EOF
+
+#
+echo "##############################################################" >> ${OUT}
+echo "WGS84 (2D), promoted to 3D -> WGS84+EGM96" >> ${OUT}
+#
+$EXE --3d +init=epsg:4326 +to +init=epsg:4326 +geoidgrids=egm96_15.gtx -E >>${OUT} <<EOF
+2dE 49dN 0
+EOF
+
 # Cleanup
 rm -rf "dir with \" space"
 
diff --git a/test/cli/testprojinfo b/test/cli/testprojinfo
index 2f8c1de5..016850a7 100755
--- a/test/cli/testprojinfo
+++ b/test/cli/testprojinfo
@@ -148,8 +148,8 @@ echo "Testing -s EPSG:4936 -t EPSG:4978 --spatial-test intersects --summary wher
 $EXE -s EPSG:4936 -t EPSG:4978 --spatial-test intersects --summary >>${OUT} 2>&1
 echo "" >>${OUT}
 
-echo "Testing -s "+proj=longlat +datum=WGS84 +geoidgrids=@foo.gtx +type=crs" -t EPSG:4326 -o PROJ -q" >> ${OUT}
-$EXE -s "+proj=longlat +datum=WGS84 +geoidgrids=@foo.gtx +type=crs" -t EPSG:4326 -o PROJ -q >>${OUT} 2>&1
+echo "Testing -s "+proj=longlat +datum=WGS84 +geoidgrids=@foo.gtx +type=crs" -t EPSG:4979 -o PROJ -q" >> ${OUT}
+$EXE -s "+proj=longlat +datum=WGS84 +geoidgrids=@foo.gtx +type=crs" -t EPSG:4979 -o PROJ -q >>${OUT} 2>&1
 echo "" >>${OUT}
 
 echo 'Testing -s "AGD66" -t "WGS 84 (G1762)" --spatial-test intersects --summary. Should include a transformation through GDA2020' >> ${OUT}
diff --git a/test/cli/testprojinfo_out.dist b/test/cli/testprojinfo_out.dist
index cb80bdd0..952c6b38 100644
--- a/test/cli/testprojinfo_out.dist
+++ b/test/cli/testprojinfo_out.dist
@@ -1243,10 +1243,8 @@ PROJCRS["WGS 84 / UTM zone 31N",
     REMARK["Promoted to 3D from EPSG:32631"]]
 
 Testing -s EPSG:32631 -t EPSG:4326+3855 --summary
-Candidate operations found: 3
-unknown id, Inverse of UTM zone 31N + WGS 84 to EGM2008 height (1), 1 m, World.
-unknown id, Inverse of UTM zone 31N + WGS 84 to EGM2008 height (2), 0.5 m, World.
-unknown id, Inverse of UTM zone 31N + Inverse of Transformation from EGM2008 height to WGS 84 (ballpark vertical transformation, without ellipsoid height to vertical height correction), unknown accuracy, World, has ballpark transformation
+Candidate operations found: 1
+unknown id, Inverse of UTM zone 31N + Inverse of Null geographic offset from WGS 84 to WGS 84, 0 m, World.
 
 Testing -s EPSG:32631 -t EPSG:4326+3855 --3d --summary
 Candidate operations found: 3
@@ -1262,7 +1260,7 @@ Candidate operations found: 2
 unknown id, Ballpark geocentric translation from ETRS89 to WGS 84, unknown accuracy, World, has ballpark transformation
 INVERSE(EPSG):9225, Inverse of WGS 84 to ETRS89 (2), 0.1 m, Germany - offshore North Sea. Netherlands - offshore east of 5E.
 
-Testing -s +proj=longlat +datum=WGS84 +geoidgrids=@foo.gtx +type=crs -t EPSG:4326 -o PROJ -q
+Testing -s +proj=longlat +datum=WGS84 +geoidgrids=@foo.gtx +type=crs -t EPSG:4979 -o PROJ -q
 +proj=pipeline
   +step +proj=unitconvert +xy_in=deg +xy_out=rad
   +step +proj=vgridshift +grids=@foo.gtx +multiplier=1
diff --git a/test/unit/test_network.cpp b/test/unit/test_network.cpp
index f8b70ae8..73265008 100644
--- a/test/unit/test_network.cpp
+++ b/test/unit/test_network.cpp
@@ -1146,7 +1146,7 @@ TEST(networking, curl_vgridshift) {
 
     // WGS84 to EGM2008 height. Using egm08_25.tif
     auto P =
-        proj_create_crs_to_crs(ctx, "EPSG:4326", "EPSG:4326+3855", nullptr);
+        proj_create_crs_to_crs(ctx, "EPSG:4979", "EPSG:4326+3855", nullptr);
     ASSERT_NE(P, nullptr);
 
     PJ_COORD c;
diff --git a/test/unit/test_operationfactory.cpp b/test/unit/test_operationfactory.cpp
index 0c3ecae4..bb69e347 100644
--- a/test/unit/test_operationfactory.cpp
+++ b/test/unit/test_operationfactory.cpp
@@ -5441,7 +5441,9 @@ TEST(operation, compoundCRS_to_geogCRS_2D_promote_to_3D_context) {
     auto src = nn_dynamic_pointer_cast<CRS>(srcObj);
     ASSERT_TRUE(src != nullptr);
     auto nnSrc = NN_NO_CHECK(src);
-    auto dst = authFactory->createCoordinateReferenceSystem("4269"); // NAD83
+    auto dst =
+        authFactory->createCoordinateReferenceSystem("4269")->promoteTo3D(
+            std::string(), authFactory->databaseContext()); // NAD83
 
     auto listCompoundToGeog2D =
         CoordinateOperationFactory::create()->createOperations(nnSrc, dst,
@@ -5454,18 +5456,11 @@ TEST(operation, compoundCRS_to_geogCRS_2D_promote_to_3D_context) {
         CoordinateOperationFactory::create()->createOperations(dst, nnSrc,
                                                                ctxt);
     EXPECT_EQ(listGeog2DToCompound.size(), listCompoundToGeog2D.size());
-
-    auto listCompoundToGeog3D =
-        CoordinateOperationFactory::create()->createOperations(
-            nnSrc,
-            dst->promoteTo3D(std::string(), authFactory->databaseContext()),
-            ctxt);
-    EXPECT_EQ(listCompoundToGeog3D.size(), listCompoundToGeog2D.size());
 }
 
 // ---------------------------------------------------------------------------
 
-TEST(operation, compoundCRS_of_projCRS_to_geogCRS_2D_context) {
+TEST(operation, compoundCRS_of_projCRS_to_geogCRS_3D_context) {
     auto authFactory =
         AuthorityFactory::create(DatabaseContext::create(), "EPSG");
     auto ctxt = CoordinateOperationContext::create(authFactory, nullptr, 0.0);
@@ -5480,7 +5475,9 @@ TEST(operation, compoundCRS_of_projCRS_to_geogCRS_2D_context) {
     auto src = nn_dynamic_pointer_cast<CRS>(srcObj);
     ASSERT_TRUE(src != nullptr);
     auto nnSrc = NN_NO_CHECK(src);
-    auto dst = authFactory->createCoordinateReferenceSystem("4269"); // NAD83
+    auto dst =
+        authFactory->createCoordinateReferenceSystem("4269")->promoteTo3D(
+            std::string(), authFactory->databaseContext()); // NAD83
 
     auto list = CoordinateOperationFactory::create()->createOperations(
         nnSrc, dst, ctxt);
@@ -5945,7 +5942,9 @@ TEST(operation, compoundCRS_of_vertCRS_with_geoid_model_to_geogCRS) {
         createFromUserInput(wkt, authFactory->databaseContext(), false);
     auto src = nn_dynamic_pointer_cast<CRS>(srcObj);
     ASSERT_TRUE(src != nullptr);
-    auto dst = authFactory->createCoordinateReferenceSystem("4269"); // NAD83
+    auto dst =
+        authFactory->createCoordinateReferenceSystem("4269")->promoteTo3D(
+            std::string(), authFactory->databaseContext()); // NAD83
 
     auto list = CoordinateOperationFactory::create()->createOperations(
         NN_NO_CHECK(src), dst, ctxt);
@@ -6153,7 +6152,7 @@ TEST(operation, compoundCRS_with_non_meter_horiz_and_vertical_to_geog) {
         AuthorityFactory::create(DatabaseContext::create(), "EPSG");
     auto ctxt = CoordinateOperationContext::create(authFactory, nullptr, 0.0);
     auto list = CoordinateOperationFactory::create()->createOperations(
-        NN_NO_CHECK(src), authFactory->createCoordinateReferenceSystem("4326"),
+        NN_NO_CHECK(src), authFactory->createCoordinateReferenceSystem("4979"),
         ctxt);
     ASSERT_EQ(list.size(), 1U);
     // Check that vertical unit conversion is done just once