2 files changed, 125 insertions, 0 deletions

diff --git a/src/iso19111/c_api.cpp b/src/iso19111/c_api.cpp
index ce7f2ae2..f8d9e685 100644
--- a/src/iso19111/c_api.cpp
+++ b/src/iso19111/c_api.cpp
@@ -9162,3 +9162,46 @@ PROJ_STRING_LIST proj_get_insert_statements(
     }
     return nullptr;
 }
+
+// ---------------------------------------------------------------------------
+
+/** \brief Returns a list of geoid models available for that crs
+ *
+ * The list includes the geoid models connected directly with the crs,
+ * or via "Height Depth Reversal" or "Change of Vertical Unit" transformations.
+ * The returned list is NULL terminated and must be freed with
+ * proj_string_list_destroy().
+ *
+ * @param ctx Context, or NULL for default context.
+ * @param auth_name Authority name (must not be NULL)
+ * @param code Object code (must not be NULL)
+ * @param options should be set to NULL for now
+ * @return list of geoid models names (to be freed with
+ * proj_string_list_destroy()), or NULL in case of error.
+ * @since 8.1
+ */
+PROJ_STRING_LIST
+proj_get_geoid_models_from_database(PJ_CONTEXT *ctx, const char *auth_name,
+                                    const char *code,
+                                    const char *const *options) {
+    SANITIZE_CTX(ctx);
+    if (!auth_name || !code) {
+        proj_context_errno_set(ctx, PROJ_ERR_OTHER_API_MISUSE);
+        proj_log_error(ctx, __FUNCTION__, "missing required input");
+        return nullptr;
+    }
+    (void)options;
+    try {
+        const std::string codeStr(code);
+        auto factory = AuthorityFactory::create(getDBcontext(ctx), auth_name);
+        auto geoidModels = factory->getGeoidModels(codeStr);
+        ctx->safeAutoCloseDbIfNeeded();
+        return to_string_list(std::move(geoidModels));
+    } catch (const std::exception &e) {
+        proj_log_error(ctx, __FUNCTION__, e.what());
+    }
+    ctx->safeAutoCloseDbIfNeeded();
+    return nullptr;
+}
+
+// ---------------------------------------------------------------------------
diff --git a/src/iso19111/factory.cpp b/src/iso19111/factory.cpp
index fabf57e1..d95ccbf4 100644
--- a/src/iso19111/factory.cpp
+++ b/src/iso19111/factory.cpp
@@ -5765,6 +5765,88 @@ AuthorityFactory::createFromCoordinateReferenceSystemCodes(
 
 // ---------------------------------------------------------------------------
 
+/** \brief Returns a list of geoid models available for that crs
+ *
+ * The list includes the geoid models connected directly with the crs,
+ * or via "Height Depth Reversal" or "Change of Vertical Unit" transformations
+ *
+ * @param code crs code allocated by authority.
+ * @return list of geoid model names
+ * @throw FactoryException
+ */
+
+std::list<std::string>
+AuthorityFactory::getGeoidModels(const std::string &code) const {
+
+    ListOfParams params;
+    std::string sql;
+    sql += "SELECT DISTINCT GM0.name "
+           " FROM geoid_model GM0 "
+           "INNER JOIN grid_transformation GT0 "
+           " ON  GT0.code = GM0.operation_code "
+           " AND GT0.auth_name = GM0.operation_auth_name "
+           " AND GT0.target_crs_code = ? ";
+    params.emplace_back(code);
+    if (d->hasAuthorityRestriction()) {
+        sql += " AND GT0.target_crs_auth_name = ? ";
+        params.emplace_back(d->authority());
+    }
+
+    /// The second part of the query is for CRSs that use that geoid model via
+    /// Height Depth Reversal (EPSG:1068) or Change of Vertical Unit (EPSG:1069)
+    sql += "UNION "
+           "SELECT DISTINCT GM0.name "
+           " FROM geoid_model GM0 "
+           "INNER JOIN grid_transformation GT1 "
+           " ON  GT1.code = GM0.operation_code "
+           " AND GT1.auth_name = GM0.operation_auth_name "
+           "INNER JOIN other_transformation OT1 "
+           " ON  OT1.source_crs_code = GT1.target_crs_code "
+           " AND OT1.source_crs_auth_name = GT1.target_crs_auth_name "
+           " AND OT1.method_auth_name = 'EPSG' "
+           " AND OT1.method_code IN (1068, 1069, 1104) "
+           " AND OT1.target_crs_code = ? ";
+    params.emplace_back(code);
+    if (d->hasAuthorityRestriction()) {
+        sql += " AND OT1.target_crs_auth_name = ? ";
+        params.emplace_back(d->authority());
+    }
+
+    /// The third part of the query is for CRSs that use that geoid model via
+    /// other_transformation table twice, like transforming depth and feet
+    sql += "UNION "
+           "SELECT DISTINCT GM0.name "
+           " FROM geoid_model GM0 "
+           "INNER JOIN grid_transformation GT1 "
+           " ON  GT1.code = GM0.operation_code "
+           " AND GT1.auth_name = GM0.operation_auth_name "
+           "INNER JOIN other_transformation OT1 "
+           " ON  OT1.source_crs_code = GT1.target_crs_code "
+           " AND OT1.source_crs_auth_name = GT1.target_crs_auth_name "
+           " AND OT1.method_auth_name = 'EPSG' "
+           " AND OT1.method_code IN (1068, 1069, 1104) "
+           "INNER JOIN other_transformation OT2 "
+           " ON  OT2.source_crs_code = OT1.target_crs_code "
+           " AND OT2.source_crs_auth_name = OT1.target_crs_auth_name "
+           " AND OT2.method_code IN (1068, 1069, 1104) "
+           " AND OT2.target_crs_code = ? ";
+    params.emplace_back(code);
+    if (d->hasAuthorityRestriction()) {
+        sql += " AND OT2.target_crs_auth_name = ? ";
+        params.emplace_back(d->authority());
+    }
+    sql += " ORDER BY 1 ";
+
+    auto sqlRes = d->run(sql, params);
+    std::list<std::string> res;
+    for (const auto &row : sqlRes) {
+        res.push_back(row[0]);
+    }
+    return res;
+}
+
+// ---------------------------------------------------------------------------
+
 /** \brief Returns a list operation::CoordinateOperation between two CRS.
  *
  * The list is ordered with preferred operations first. No attempt is made