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-rw-r--r--src/iso19111/c_api.cpp5
1 files changed, 5 insertions, 0 deletions
diff --git a/src/iso19111/c_api.cpp b/src/iso19111/c_api.cpp
index fd4090b2..090d59a1 100644
--- a/src/iso19111/c_api.cpp
+++ b/src/iso19111/c_api.cpp
@@ -7080,6 +7080,11 @@ void PROJ_DLL proj_operation_factory_context_set_discard_superseded(
* by increasing accuracy. Operations with unknown accuracy are sorted last,
* whatever their area.
*
+ * When one of the source or target CRS has a vertical component but not the
+ * other one, the one that has no vertical component is automatically promoted
+ * to a 3D version, where its vertical axis is the ellipsoidal height in metres,
+ * using the ellipsoid of the base geodetic CRS.
+ *
* @param ctx PROJ context, or NULL for default context
* @param source_crs source CRS. Must not be NULL.
* @param target_crs source CRS. Must not be NULL.