diff --git a/.gitignore b/.gitignore
index a2bb453b..6b099c07 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,3 +14,4 @@ COLCON_IGNORE
 .catkin_tools
 core
 /tmp
+/prompt.md
diff --git a/fixposition-sdk b/fixposition-sdk
index 8c37c260..3a664467 160000
--- a/fixposition-sdk
+++ b/fixposition-sdk
@@ -1 +1 @@
-Subproject commit 8c37c260beeebe0fe26738c469f1806430f9f19d
+Subproject commit 3a664467b64a69a47ba292ed00f346232f75f0fe
diff --git a/fixposition_driver_lib/CMakeLists.txt b/fixposition_driver_lib/CMakeLists.txt
index c52ac2d4..689fed54 100644
--- a/fixposition_driver_lib/CMakeLists.txt
+++ b/fixposition_driver_lib/CMakeLists.txt
@@ -45,7 +45,35 @@ add_library(
   src/params.cpp
 )
 
-target_link_libraries(${PROJECT_NAME} ${Boost_LIBRARIES} ${fpsdk_common_LIBRARIES} pthread)
+target_link_libraries(${PROJECT_NAME}
+  ${Boost_LIBRARIES}
+  ${fpsdk_common_LIBRARIES}
+  pthread
+)
+
+
+# TESTS =================================================================================================================
+
+# Defines BUILD_TESTING (default ON), calls enable_testing()
+include(CTest)
+
+# Build tests only if GTest is available
+if(BUILD_TESTING)
+  find_package(GTest 1.11.0 QUIET)
+  if(GTest_FOUND)
+    add_executable(${PROJECT_NAME}_llh_trafo_test
+      test/llh_trafo_test.cpp
+    )
+    target_link_libraries(${PROJECT_NAME}_llh_trafo_test
+      PRIVATE
+        ${PROJECT_NAME}
+        GTest::gtest_main
+    )
+    add_test(NAME ${PROJECT_NAME}_llh_trafo_test COMMAND ${PROJECT_NAME}_llh_trafo_test)
+  else()
+    message(STATUS "${PROJECT_NAME}: GTest not found, not building tests")
+  endif()
+endif()
 
 
 # INSTALL ==============================================================================================================
diff --git a/fixposition_driver_lib/cmake/fixposition_driver_lib-config.cmake.in b/fixposition_driver_lib/cmake/fixposition_driver_lib-config.cmake.in
index cb4bbf37..36429b8b 100644
--- a/fixposition_driver_lib/cmake/fixposition_driver_lib-config.cmake.in
+++ b/fixposition_driver_lib/cmake/fixposition_driver_lib-config.cmake.in
@@ -1,5 +1,11 @@
 @PACKAGE_INIT@
 
+include(CMakeFindDependencyMacro)
+set(_fixposition_driver_lib_package_prefix_dir "${PACKAGE_PREFIX_DIR}")
+find_dependency(fpsdk_common)
+set(PACKAGE_PREFIX_DIR "${_fixposition_driver_lib_package_prefix_dir}")
+unset(_fixposition_driver_lib_package_prefix_dir)
+
 set(@PROJECT_NAME@_FOUND ON)
 set_and_check(@PROJECT_NAME@_INCLUDE_DIRS "${PACKAGE_PREFIX_DIR}/include")
 set_and_check(@PROJECT_NAME@_LIBRARY_DIRS "${PACKAGE_PREFIX_DIR}/lib")
diff --git a/fixposition_driver_lib/include/fixposition_driver_lib/helper.hpp b/fixposition_driver_lib/include/fixposition_driver_lib/helper.hpp
index 466d903a..56e94bf2 100644
--- a/fixposition_driver_lib/include/fixposition_driver_lib/helper.hpp
+++ b/fixposition_driver_lib/include/fixposition_driver_lib/helper.hpp
@@ -16,6 +16,7 @@
 
 /* LIBC/STL */
 #include <cstdint>
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -27,6 +28,7 @@
 #include <fpsdk_common/parser/nmea.hpp>
 #include <fpsdk_common/parser/novb.hpp>
 #include <fpsdk_common/time.hpp>
+#include <fpsdk_common/trafo.hpp>
 
 /* PACKAGE */
 #include "fixposition_driver_lib/params.hpp"
@@ -307,6 +309,35 @@ struct FusionEpochData {
     FusionEpochData CompleteAndReset(const fpsdk::common::parser::fpa::FpaEoePayload& eoe);
 };
 
+#if FPSDK_USE_PROJ
+/**
+ * @brief Initialise ECEF to LLH transformer
+ *
+ * Creates a PROJ transformer (see fpsdk::common::trafo::Transformer) if params.datum_llh_enabled_ is true. The source
+ * CRS must be geocentric. The target CRS must be either geographic 3D, or compound geographic 2D plus vertical.
+ *
+ * @param[in]  params     Driver parameters (datum_llh_...)
+ * @param[out] llh_trafo  The transformer, nullptr if disabled
+ * @param[out] error      Error message, on failure
+ *
+ * @returns true if disabled or if the transformer is valid, false otherwise
+ */
+bool InitLlhTrafo(const DriverParams& params, std::unique_ptr<fpsdk::common::trafo::Transformer>& llh_trafo,
+                  std::string& error);
+
+/**
+ * @brief Convert ECEF to latitude, longitude and height
+ *
+ * @param[in]  llh_trafo  Transformer from InitLlhTrafo(), nullptr to use the built-in WGS84 conversion
+ * @param[in]  ecef       ECEF position [m]
+ * @param[out] llh_rad    Latitude [rad], longitude [rad], height [m]
+ *
+ * @returns true on success, false if the transformation failed
+ */
+bool EcefToLlhRad(const fpsdk::common::trafo::Transformer* llh_trafo, const Eigen::Vector3d& ecef,
+                  Eigen::Vector3d& llh_rad);
+#endif  // FPSDK_USE_PROJ
+
 void HelloWorld();
 
 /* ****************************************************************************************************************** */
diff --git a/fixposition_driver_lib/include/fixposition_driver_lib/params.hpp b/fixposition_driver_lib/include/fixposition_driver_lib/params.hpp
index 331c6865..cf42af67 100644
--- a/fixposition_driver_lib/include/fixposition_driver_lib/params.hpp
+++ b/fixposition_driver_lib/include/fixposition_driver_lib/params.hpp
@@ -41,6 +41,9 @@ struct DriverParams {
     bool raw_output_ = false;
     bool cov_warning_ = false;
     bool nav2_mode_ = false;
+    bool datum_llh_enabled_ = false;
+    std::string datum_llh_ecef_crs_ = "EPSG:4978";
+    std::string datum_llh_llh_crs_ = "EPSG:4979";
 
     enum class VelTopicType { UNSPECIFIED, TWIST, TWISTWITHCOV, ODOMETRY };
     bool converter_enabled_ = false;
diff --git a/fixposition_driver_lib/src/helper.cpp b/fixposition_driver_lib/src/helper.cpp
index 232c4a8e..c863db69 100644
--- a/fixposition_driver_lib/src/helper.cpp
+++ b/fixposition_driver_lib/src/helper.cpp
@@ -12,10 +12,12 @@
  */
 
 /* LIBC/STL */
+#include <atomic>
 #include <utility>
 
 /* EXTERNAL */
 #include <fpsdk_common/logging.hpp>
+#include <fpsdk_common/math.hpp>
 #include <fpsdk_common/parser/crc.hpp>
 #include <fpsdk_common/string.hpp>
 #include <fpsdk_common/trafo.hpp>
@@ -161,13 +163,12 @@ bool OdometryData::ConvertToEnu(const TfData& tf_ecef_enu0) {
     const Eigen::Matrix<double, 6, 6> cov_ecef = pose.cov;
 
     // Extract data from the TF message (using the arrow operator)
-    const Eigen::Vector3d t_ecef_enu0 = tf_ecef_enu0.translation;
     const Eigen::Quaterniond q_ecef_enu0 = tf_ecef_enu0.rotation;
     const Eigen::Matrix3d rot_ecef_enu0 = q_ecef_enu0.toRotationMatrix();
 
     // Convert position in ECEF into position in ENU
-    const Eigen::Vector3d t_enu_body =
-        fpsdk::common::trafo::TfEnuEcef(t_ecef_body, fpsdk::common::trafo::TfWgs84LlhEcef(t_ecef_enu0));
+    const Eigen::Vector3d wgs84llh_ref = fpsdk::common::trafo::TfWgs84LlhEcef(tf_ecef_enu0.translation);
+    const Eigen::Vector3d t_enu_body = fpsdk::common::trafo::TfEnuEcef(t_ecef_body, wgs84llh_ref);
     const Eigen::Quaterniond q_enu_body = q_ecef_enu0.inverse() * q_ecef_body;
 
     // Convert covariance matrix to ENU
@@ -415,6 +416,63 @@ FusionEpochData FusionEpochData::CompleteAndReset(const fpsdk::common::parser::f
 
 // ---------------------------------------------------------------------------------------------------------------------
 
+#if FPSDK_USE_PROJ
+bool InitLlhTrafo(const DriverParams& params, std::unique_ptr<trafo::Transformer>& llh_trafo, std::string& error) {
+    llh_trafo.reset();
+    error.clear();
+    if (!params.datum_llh_enabled_) {
+        return true;
+    }
+
+    // Normalized output has longitude, latitude and height order regardless of the CRS's native axis order.
+    trafo::TransformerOpts opts;
+    opts.precise_ = true;
+    opts.normalize_axes_ = true;
+    auto new_trafo = std::make_unique<trafo::Transformer>("datum_llh");
+    if (!new_trafo->Init(params.datum_llh_ecef_crs_, params.datum_llh_llh_crs_, opts)) {
+        error = "invalid CRS or transformation unavailable";
+        return false;
+    }
+
+    const auto source = new_trafo->SourceCrs();
+    const auto target = new_trafo->TargetCrs();
+    if (source.type_ != trafo::CrsType::GEOCENTRIC) {
+        error = "source CRS must be geocentric";
+        return false;
+    }
+    const std::vector<trafo::CrsType> geo2d_vertical = {trafo::CrsType::GEOGRAPHIC_2D, trafo::CrsType::VERTICAL};
+    if (!((target.type_ == trafo::CrsType::GEOGRAPHIC_3D) ||
+          ((target.type_ == trafo::CrsType::COMPOUND) && (target.sub_types_ == geo2d_vertical)))) {
+        error = "target CRS must be geographic 3D or geographic 2D plus vertical";
+        return false;
+    }
+
+    llh_trafo = std::move(new_trafo);
+    return true;
+}
+
+bool EcefToLlhRad(const trafo::Transformer* llh_trafo, const Eigen::Vector3d& ecef, Eigen::Vector3d& llh_rad) {
+    if (llh_trafo == nullptr) {
+        llh_rad = trafo::TfWgs84LlhEcef(ecef);
+        return true;
+    }
+
+    Eigen::Vector3d lonlath;
+    if (!llh_trafo->Transform(ecef, lonlath)) {
+        // Report only once
+        static std::atomic<bool> warned = false;
+        if (!warned.exchange(true)) {
+            WARNING("PROJ ECEF to LLH transformation failed");
+        }
+        return false;
+    }
+    llh_rad = {math::DegToRad(lonlath.y()), math::DegToRad(lonlath.x()), lonlath.z()};
+    return true;
+}
+#endif  // FPSDK_USE_PROJ
+
+// ---------------------------------------------------------------------------------------------------------------------
+
 void HelloWorld() {
     NOTICE("Fixposition driver (https://github.com/fixposition/fixposition_driver)");
     NOTICE("Fixposition SDK %s", utils::GetVersionString());
diff --git a/fixposition_driver_lib/test/llh_trafo_test.cpp b/fixposition_driver_lib/test/llh_trafo_test.cpp
new file mode 100644
index 00000000..368618ff
--- /dev/null
+++ b/fixposition_driver_lib/test/llh_trafo_test.cpp
@@ -0,0 +1,127 @@
+/**
+ * \verbatim
+ * ___    ___
+ * \  \  /  /
+ *  \  \/  /   Copyright (c) Fixposition AG (www.fixposition.com) and contributors
+ *  /  /\  \   License: see the LICENSE file
+ * /__/  \__\
+ * \endverbatim
+ */
+
+/* LIBC/STL */
+#include <memory>
+#include <string>
+#include <thread>
+
+/* EXTERNAL */
+#include <gtest/gtest.h>
+
+#include <fpsdk_common/math.hpp>
+#include <fpsdk_common/trafo.hpp>
+
+/* PACKAGE */
+#include "fixposition_driver_lib/helper.hpp"
+#include "fixposition_driver_lib/params.hpp"
+
+namespace fixposition {
+/* ****************************************************************************************************************** */
+
+TEST(LlhTrafo, ParamsUseWgs84ThreeDimensionalDefaults) {
+    const DriverParams params;
+    EXPECT_FALSE(params.datum_llh_enabled_);
+    EXPECT_EQ(params.datum_llh_ecef_crs_, "EPSG:4978");
+    EXPECT_EQ(params.datum_llh_llh_crs_, "EPSG:4979");
+}
+
+TEST(OdometryData, EnuOriginAlwaysUsesEllipsoidalWgs84Height) {
+    const Eigen::Vector3d llh_ref(fpsdk::common::math::DegToRad(47.0), fpsdk::common::math::DegToRad(8.0), 500.0);
+    const Eigen::Vector3d ecef_ref = fpsdk::common::trafo::TfEcefWgs84Llh(llh_ref);
+
+    TfData tf;
+    tf.valid = true;
+    tf.translation = ecef_ref;
+    tf.rotation.setIdentity();
+
+    OdometryData odometry;
+    odometry.pose.position = ecef_ref;
+    odometry.pose.orientation.setIdentity();
+    ASSERT_TRUE(odometry.ConvertToEnu(tf));
+    EXPECT_LT(odometry.pose.position.norm(), 1e-3) << odometry.pose.position.transpose();
+}
+
+#if FPSDK_USE_PROJ
+using fpsdk::common::trafo::Transformer;
+
+// Driver params with datum LLH enabled
+static DriverParams LlhParams(const std::string& ecef_crs, const std::string& llh_crs) {
+    DriverParams params;
+    params.datum_llh_enabled_ = true;
+    params.datum_llh_ecef_crs_ = ecef_crs;
+    params.datum_llh_llh_crs_ = llh_crs;
+    return params;
+}
+
+TEST(LlhTrafo, DisabledUsesBuiltInWgs84Conversion) {
+    DriverParams params;
+    params.datum_llh_ecef_crs_ = "not a CRS";
+    params.datum_llh_llh_crs_ = "also not a CRS";
+    std::unique_ptr<Transformer> llh_trafo;
+    std::string error;
+    ASSERT_TRUE(InitLlhTrafo(params, llh_trafo, error));
+    EXPECT_FALSE(llh_trafo);
+    EXPECT_TRUE(error.empty());
+
+    const Eigen::Vector3d expected_llh(fpsdk::common::math::DegToRad(47.0), fpsdk::common::math::DegToRad(8.0), 500.0);
+    const Eigen::Vector3d ecef = fpsdk::common::trafo::TfEcefWgs84Llh(expected_llh);
+    Eigen::Vector3d actual_llh;
+    ASSERT_TRUE(EcefToLlhRad(llh_trafo.get(), ecef, actual_llh));
+    EXPECT_TRUE(actual_llh.isApprox(expected_llh, 1e-8));
+}
+
+TEST(LlhTrafo, RejectsInvalidAndNonGeographicCrs) {
+    std::unique_ptr<Transformer> llh_trafo;
+    std::string error;
+    EXPECT_FALSE(InitLlhTrafo(LlhParams("EPSG:4978", "EPSG:4979+3855"), llh_trafo, error));
+    EXPECT_FALSE(llh_trafo);
+    EXPECT_FALSE(error.empty());
+    EXPECT_FALSE(InitLlhTrafo(LlhParams("EPSG:4978", "EPSG:2056"), llh_trafo, error));
+    EXPECT_FALSE(llh_trafo);
+    EXPECT_EQ(error, "target CRS must be geographic 3D or geographic 2D plus vertical");
+    EXPECT_FALSE(InitLlhTrafo(LlhParams("EPSG:4326", "EPSG:4979"), llh_trafo, error));
+    EXPECT_FALSE(llh_trafo);
+    EXPECT_EQ(error, "source CRS must be geocentric");
+}
+
+TEST(LlhTrafo, MatchesBuiltInWgs84Conversion) {
+    std::unique_ptr<Transformer> llh_trafo;
+    std::string error;
+    ASSERT_TRUE(InitLlhTrafo(LlhParams("EPSG:4978", "EPSG:4979"), llh_trafo, error)) << error;
+    ASSERT_TRUE(llh_trafo);
+
+    // Checks lon/lat swap and deg to rad
+    const Eigen::Vector3d expected_llh(fpsdk::common::math::DegToRad(47.0), fpsdk::common::math::DegToRad(8.0), 500.0);
+    const Eigen::Vector3d ecef = fpsdk::common::trafo::TfEcefWgs84Llh(expected_llh);
+    Eigen::Vector3d actual_llh;
+    ASSERT_TRUE(EcefToLlhRad(llh_trafo.get(), ecef, actual_llh));
+    EXPECT_TRUE(actual_llh.isApprox(expected_llh, 1e-8)) << actual_llh.transpose();
+}
+
+TEST(LlhTrafo, TransformsOnAThreadDifferentFromInitialization) {
+    std::unique_ptr<Transformer> llh_trafo;
+    std::string error;
+    ASSERT_TRUE(InitLlhTrafo(LlhParams("EPSG:4978", "EPSG:4979"), llh_trafo, error)) << error;
+
+    const Eigen::Vector3d expected_llh(fpsdk::common::math::DegToRad(47.0), fpsdk::common::math::DegToRad(8.0), 500.0);
+    const Eigen::Vector3d ecef = fpsdk::common::trafo::TfEcefWgs84Llh(expected_llh);
+    Eigen::Vector3d actual_llh;
+    bool success = false;
+    std::thread worker([&]() { success = EcefToLlhRad(llh_trafo.get(), ecef, actual_llh); });
+    worker.join();
+
+    ASSERT_TRUE(success);
+    EXPECT_TRUE(actual_llh.isApprox(expected_llh, 1e-8));
+}
+#endif
+
+/* ****************************************************************************************************************** */
+}  // namespace fixposition
diff --git a/fixposition_driver_ros1/include/fixposition_driver_ros1/data_to_ros1.hpp b/fixposition_driver_ros1/include/fixposition_driver_ros1/data_to_ros1.hpp
index 6ef1e550..78a49e3c 100644
--- a/fixposition_driver_ros1/include/fixposition_driver_ros1/data_to_ros1.hpp
+++ b/fixposition_driver_ros1/include/fixposition_driver_ros1/data_to_ros1.hpp
@@ -15,7 +15,6 @@
 #define __FIXPOSITION_DRIVER_ROS1_DATA_TO_ROS1_HPP__
 
 /* LIBC/STL */
-#include <memory>
 #include <unordered_map>
 
 /* EXTERNAL */
@@ -39,6 +38,9 @@ void PublishFpaOdometry(const fpsdk::common::parser::fpa::FpaOdometryPayload& pa
 void PublishFpaOdometryDataImu(const fpsdk::common::parser::fpa::FpaOdometryPayload& payload, bool nav2_mode_,
                                ros::Publisher& pub);
 void PublishFpaOdometryDataNavSatFix(const fpsdk::common::parser::fpa::FpaOdometryPayload& payload, bool nav2_mode_,
+#if FPSDK_USE_PROJ
+                                     const fpsdk::common::trafo::Transformer* llh_trafo,
+#endif
                                      ros::Publisher& pub);
 void PublishFpaOdomenu(const fpsdk::common::parser::fpa::FpaOdomenuPayload& payload, ros::Publisher& pub);
 void PublishFpaOdomenuVector3Stamped(const fpsdk::common::parser::fpa::FpaOdomenuPayload& payload, ros::Publisher& pub);
@@ -77,7 +79,11 @@ void PublishParserMsg(const fpsdk::common::parser::ParserMsg& msg, ros::Publishe
 void PublishNmeaEpochData(const NmeaEpochData& data, ros::Publisher& pub);
 void PublishOdometryData(const OdometryData& data, ros::Publisher& pub);
 void PublishJumpWarning(const JumpDetector& jump_detector, ros::Publisher& pub);
-void PublishDatum(const geometry_msgs::Vector3& payload, const ros::Time& stamp, ros::Publisher& pub);
+void PublishDatum(const geometry_msgs::Vector3& payload, const ros::Time& stamp,
+#if FPSDK_USE_PROJ
+                  const fpsdk::common::trafo::Transformer* llh_trafo,
+#endif
+                  ros::Publisher& pub);
 void PublishFusionEpochData(const FusionEpochData& data, ros::Publisher& pub);
 
 /* ****************************************************************************************************************** */
diff --git a/fixposition_driver_ros1/include/fixposition_driver_ros1/fixposition_driver_node.hpp b/fixposition_driver_ros1/include/fixposition_driver_ros1/fixposition_driver_node.hpp
index 3581ade3..02bde18a 100644
--- a/fixposition_driver_ros1/include/fixposition_driver_ros1/fixposition_driver_node.hpp
+++ b/fixposition_driver_ros1/include/fixposition_driver_ros1/fixposition_driver_node.hpp
@@ -63,6 +63,10 @@ class FixpositionDriverNode {
     DriverParams params_;       //!< Sensor/driver parameters
     FixpositionDriver driver_;  //!< Sensor driver
 
+#if FPSDK_USE_PROJ
+    std::unique_ptr<fpsdk::common::trafo::Transformer> llh_trafo_;  //!< ECEF to LLH, nullptr = built-in WGS84
+#endif
+
     // ROS publishers
     // - FP_A messages
     ros::Publisher fpa_eoe_pub_;         //!< FP_A-EOE message
diff --git a/fixposition_driver_ros1/launch/config.yaml b/fixposition_driver_ros1/launch/config.yaml
index fb65e611..957b39f8 100644
--- a/fixposition_driver_ros1/launch/config.yaml
+++ b/fixposition_driver_ros1/launch/config.yaml
@@ -54,6 +54,13 @@ raw_output:   false    # Enable raw messages output
 cov_warning:  false    # Enable covariance warnings
 nav2_mode:    false    # Enable nav2 mode
 
+# Optional: omitting this block preserves the legacy WGS-84 LLH output.
+datum_llh:
+    enabled: false               # Use PROJ to convert the altitude published on odometry_llh and datum
+    ecef_crs: "EPSG:4978"        # Geocentric source CRS of the sensor's ECEF coordinates; normally do not change
+    llh_crs: "EPSG:4979"         # Geographic output CRS. For EGM2008 orthometric height use "EPSG:4326+3855"
+                                 # and install the us_nga_egm08_25.tif PROJ grid. Missing grids are treated as errors.
+
 converter:
     enabled: false
     topic_type: "Twist"        # Supported types: nav_msgs/{Twist, TwistWithCov, Odometry}
diff --git a/fixposition_driver_ros1/src/data_to_ros1.cpp b/fixposition_driver_ros1/src/data_to_ros1.cpp
index 942ba1bd..e2f8414f 100644
--- a/fixposition_driver_ros1/src/data_to_ros1.cpp
+++ b/fixposition_driver_ros1/src/data_to_ros1.cpp
@@ -153,7 +153,11 @@ void PublishFpaOdometryDataImu(const fpa::FpaOdometryPayload& payload, bool nav2
 
 // ---------------------------------------------------------------------------------------------------------------------
 
-void PublishFpaOdometryDataNavSatFix(const fpa::FpaOdometryPayload& payload, bool nav2_mode_, ros::Publisher& pub) {
+void PublishFpaOdometryDataNavSatFix(const fpa::FpaOdometryPayload& payload, bool nav2_mode_,
+#if FPSDK_USE_PROJ
+                                     const trafo::Transformer* llh_trafo,
+#endif
+                                     ros::Publisher& pub) {
     if (pub.getNumSubscribers() > 0) {
         sensor_msgs::NavSatFix msg;
         msg.header.stamp = ros1::ConvTime(FpaGpsTimeToTime(payload.gps_time));
@@ -173,14 +177,21 @@ void PublishFpaOdometryDataNavSatFix(const fpa::FpaOdometryPayload& payload, boo
             msg.position_covariance_type = msg.COVARIANCE_TYPE_UNKNOWN;
             cov_map = Eigen::Matrix3d::Zero();  // FIXME: necessary?
         } else {
-            const Eigen::Vector3d llh_pos = trafo::TfWgs84LlhEcef(pose.position);
+            Eigen::Vector3d llh_pos;
+#if FPSDK_USE_PROJ
+            if (!EcefToLlhRad(llh_trafo, pose.position, llh_pos)) {
+                return;
+            }
+#else
+            llh_pos = trafo::TfWgs84LlhEcef(pose.position);
+#endif
             msg.latitude = math::RadToDeg(llh_pos(0));
             msg.longitude = math::RadToDeg(llh_pos(1));
             msg.altitude = llh_pos(2);
 
             // Populate LLH covariance
             const Eigen::Matrix3d p_cov_e = pose.cov.topLeftCorner(3, 3);
-            const Eigen::Matrix3d C_l_e = trafo::RotEnuEcef(pose.position);
+            const Eigen::Matrix3d C_l_e = trafo::RotEnuEcef(llh_pos.x(), llh_pos.y());
             const Eigen::Matrix3d p_cov_l = C_l_e * p_cov_e * C_l_e.transpose();
             cov_map = p_cov_l;
             msg.position_covariance_type = msg.COVARIANCE_TYPE_KNOWN;
@@ -864,7 +875,11 @@ void PublishJumpWarning(const JumpDetector& jump_detector, ros::Publisher& pub)
 
 // ---------------------------------------------------------------------------------------------------------------------
 
-void PublishDatum(const geometry_msgs::Vector3& payload, const ros::Time& stamp, ros::Publisher& pub) {
+void PublishDatum(const geometry_msgs::Vector3& payload, const ros::Time& stamp,
+#if FPSDK_USE_PROJ
+                  const trafo::Transformer* llh_trafo,
+#endif
+                  ros::Publisher& pub) {
     if (pub.getNumSubscribers() > 0) {
         sensor_msgs::NavSatFix msg;
         msg.header.stamp = stamp;
@@ -872,7 +887,14 @@ void PublishDatum(const geometry_msgs::Vector3& payload, const ros::Time& stamp,
 
         // Populate LLH position
         const Eigen::Vector3d position = {payload.x, payload.y, payload.z};
-        const Eigen::Vector3d llh_pos = trafo::TfWgs84LlhEcef(position);
+        Eigen::Vector3d llh_pos;
+#if FPSDK_USE_PROJ
+        if (!EcefToLlhRad(llh_trafo, position, llh_pos)) {
+            return;
+        }
+#else
+        llh_pos = trafo::TfWgs84LlhEcef(position);
+#endif
         msg.latitude = math::RadToDeg(llh_pos(0));
         msg.longitude = math::RadToDeg(llh_pos(1));
         msg.altitude = llh_pos(2);
diff --git a/fixposition_driver_ros1/src/fixposition_driver_node.cpp b/fixposition_driver_ros1/src/fixposition_driver_node.cpp
index d5e8de60..c1306717 100644
--- a/fixposition_driver_ros1/src/fixposition_driver_node.cpp
+++ b/fixposition_driver_ros1/src/fixposition_driver_node.cpp
@@ -16,6 +16,7 @@
 #include <cstring>
 #include <functional>
 #include <memory>
+#include <stdexcept>
 #include <unordered_map>
 #include <vector>
 
@@ -45,7 +46,21 @@ FixpositionDriverNode::FixpositionDriverNode(const DriverParams& params, ros::No
     params_            { params },
     driver_            { params_ },
     nmea_epoch_data_   { params_.nmea_epoch_ }  // clang-format on
-{}
+{
+#if FPSDK_USE_PROJ
+    std::string error;
+    if (!InitLlhTrafo(params_, llh_trafo_, error)) {
+        throw std::runtime_error("Failed initializing PROJ transformation: " + error);
+    }
+    if (llh_trafo_) {
+        ROS_INFO("PROJ enabled for ECEF to LLH output conversion");
+    }
+#else
+    if (params_.datum_llh_enabled_) {
+        throw std::runtime_error("Failed initializing PROJ transformation: driver was built without PROJ support");
+    }
+#endif
+}
 
 FixpositionDriverNode::~FixpositionDriverNode() { StopNode(); }
 
@@ -81,7 +96,11 @@ bool FixpositionDriverNode::StartNode() {
             auto odometry_payload = dynamic_cast<const fpa::FpaOdometryPayload&>(payload);
             PublishFpaOdometry(odometry_payload, fpa_odometry_pub_);
             PublishFpaOdometryDataImu(odometry_payload, params_.nav2_mode_, poiimu_pub_);
+#if FPSDK_USE_PROJ
+            PublishFpaOdometryDataNavSatFix(odometry_payload, params_.nav2_mode_, llh_trafo_.get(), odometry_llh_pub_);
+#else
             PublishFpaOdometryDataNavSatFix(odometry_payload, params_.nav2_mode_, odometry_llh_pub_);
+#endif
             OdometryData odometry_data;
             odometry_data.SetFromFpaOdomPayload(odometry_payload);
             PublishOdometryData(odometry_data, odometry_ecef_pub_);
@@ -701,8 +720,12 @@ void FixpositionDriverNode::PublishNav2Tf() {
     // Send the transform
     tf_br_.sendTransform(tf_odom_base);
 
-    // Publish WGS84 datum
+    // Publish datum in the configured LLH CRS
+#if FPSDK_USE_PROJ
+    PublishDatum(trans_ecef_enu0, tfs_.enu0_poi_->header.stamp, llh_trafo_.get(), datum_pub_);
+#else
     PublishDatum(trans_ecef_enu0, tfs_.enu0_poi_->header.stamp, datum_pub_);
+#endif
 }
 
 /* ****************************************************************************************************************** */
diff --git a/fixposition_driver_ros1/src/params.cpp b/fixposition_driver_ros1/src/params.cpp
index 14a90d79..43e7f4db 100644
--- a/fixposition_driver_ros1/src/params.cpp
+++ b/fixposition_driver_ros1/src/params.cpp
@@ -37,6 +37,14 @@ static bool LoadRosParam(const std::string& name, T& value) {
     return true;
 }
 
+static bool HasRosParam(const std::string& name) {
+    try {
+        return ros::param::has(name);
+    } catch (ros::InvalidNameException& e) {
+        return false;
+    }
+}
+
 bool LoadParamsFromRos1(const std::string& ns, DriverParams& params) {
     bool ok = true;
     ROS_INFO("DriverParams: loading from %s", ns.c_str());
@@ -82,6 +90,21 @@ bool LoadParamsFromRos1(const std::string& ns, DriverParams& params) {
         ROS_WARN("Failed loading %s/nav2_mode param", ns.c_str());
         ok = false;
     }
+    // Optional, keep defaults if datum_llh absent
+    if (HasRosParam(ns + "/datum_llh")) {
+        if (!LoadRosParam(ns + "/datum_llh/enabled", params.datum_llh_enabled_)) {
+            ROS_WARN("Failed loading %s/datum_llh/enabled param", ns.c_str());
+            ok = false;
+        }
+        if (!LoadRosParam(ns + "/datum_llh/ecef_crs", params.datum_llh_ecef_crs_)) {
+            ROS_WARN("Failed loading %s/datum_llh/ecef_crs param", ns.c_str());
+            ok = false;
+        }
+        if (!LoadRosParam(ns + "/datum_llh/llh_crs", params.datum_llh_llh_crs_)) {
+            ROS_WARN("Failed loading %s/datum_llh/llh_crs param", ns.c_str());
+            ok = false;
+        }
+    }
     if (!LoadRosParam(ns + "/converter/enabled", params.converter_enabled_)) {
         ROS_WARN("Failed loading %s/converter/enabled param", ns.c_str());
         ok = false;
@@ -146,6 +169,9 @@ bool LoadParamsFromRos1(const std::string& ns, DriverParams& params) {
     ROS_INFO("DriverParams: raw_output=%s", params.raw_output_ ? "true" : "false");
     ROS_INFO("DriverParams: cov_warning=%s", params.cov_warning_ ? "true" : "false");
     ROS_INFO("DriverParams: nav2_mode=%s", params.nav2_mode_ ? "true" : "false");
+    ROS_INFO("DriverParams: datum_llh_enabled=%s", params.datum_llh_enabled_ ? "true" : "false");
+    ROS_INFO("DriverParams: datum_llh_ecef_crs=%s", params.datum_llh_ecef_crs_.c_str());
+    ROS_INFO("DriverParams: datum_llh_llh_crs=%s", params.datum_llh_llh_crs_.c_str());
     ROS_INFO("DriverParams: converter_enabled=%s", params.converter_enabled_ ? "true" : "false");
     ROS_INFO("DriverParams: converter_topic_type=%s", topic_type_string_.c_str());
     ROS_INFO("DriverParams: converter_input_topic=%s", params.converter_input_topic_.c_str());
diff --git a/fixposition_driver_ros2/include/fixposition_driver_ros2/data_to_ros2.hpp b/fixposition_driver_ros2/include/fixposition_driver_ros2/data_to_ros2.hpp
index b3f9ab35..a71e18c8 100644
--- a/fixposition_driver_ros2/include/fixposition_driver_ros2/data_to_ros2.hpp
+++ b/fixposition_driver_ros2/include/fixposition_driver_ros2/data_to_ros2.hpp
@@ -15,7 +15,6 @@
 #define __FIXPOSITION_DRIVER_ROS2_DATA_TO_ROS2_HPP__
 
 /* LIBC/STL */
-#include <memory>
 #include <unordered_map>
 
 /* EXTERNAL */
@@ -40,6 +39,9 @@ void PublishFpaOdometry(const fpsdk::common::parser::fpa::FpaOdometryPayload& pa
 void PublishFpaOdometryDataImu(const fpsdk::common::parser::fpa::FpaOdometryPayload& payload, bool nav2_mode_,
                                rclcpp::Publisher<sensor_msgs::msg::Imu>::SharedPtr& pub);
 void PublishFpaOdometryDataNavSatFix(const fpsdk::common::parser::fpa::FpaOdometryPayload& payload, bool nav2_mode_,
+#if FPSDK_USE_PROJ
+                                     const fpsdk::common::trafo::Transformer* llh_trafo,
+#endif
                                      rclcpp::Publisher<sensor_msgs::msg::NavSatFix>::SharedPtr& pub);
 void PublishFpaOdomenu(const fpsdk::common::parser::fpa::FpaOdomenuPayload& payload,
                        rclcpp::Publisher<fpmsgs::FpaOdomenu>::SharedPtr& pub);
@@ -105,6 +107,9 @@ void PublishNmeaEpochData(const NmeaEpochData& data, rclcpp::Publisher<fpmsgs::N
 void PublishOdometryData(const OdometryData& data, rclcpp::Publisher<nav_msgs::msg::Odometry>::SharedPtr& pub);
 void PublishJumpWarning(const JumpDetector& jump_detector, rclcpp::Publisher<fpmsgs::CovWarn>::SharedPtr& pub);
 void PublishDatum(const geometry_msgs::msg::Vector3& payload, const builtin_interfaces::msg::Time& stamp,
+#if FPSDK_USE_PROJ
+                  const fpsdk::common::trafo::Transformer* llh_trafo,
+#endif
                   rclcpp::Publisher<sensor_msgs::msg::NavSatFix>::SharedPtr& pub);
 void PublishFusionEpochData(const FusionEpochData& data, rclcpp::Publisher<fpmsgs::FusionEpoch>::SharedPtr& pub);
 
diff --git a/fixposition_driver_ros2/include/fixposition_driver_ros2/fixposition_driver_node.hpp b/fixposition_driver_ros2/include/fixposition_driver_ros2/fixposition_driver_node.hpp
index 44451d69..e784fc76 100644
--- a/fixposition_driver_ros2/include/fixposition_driver_ros2/fixposition_driver_node.hpp
+++ b/fixposition_driver_ros2/include/fixposition_driver_ros2/fixposition_driver_node.hpp
@@ -67,6 +67,10 @@ class FixpositionDriverNode {
     FixpositionDriver driver_;          //!< Sensor driver
     rclcpp::QoS qos_settings_;          //!< QoS settings
 
+#if FPSDK_USE_PROJ
+    std::unique_ptr<fpsdk::common::trafo::Transformer> llh_trafo_;  //!< ECEF to LLH, nullptr = built-in WGS84
+#endif
+
     // ROS publishers
     // - FP_A messages
     rclcpp::Publisher<fpmsgs::FpaEoe>::SharedPtr fpa_eoe_pub_;                //!< FP_A-EOE message
diff --git a/fixposition_driver_ros2/launch/config.yaml b/fixposition_driver_ros2/launch/config.yaml
index 6b951101..6767c796 100644
--- a/fixposition_driver_ros2/launch/config.yaml
+++ b/fixposition_driver_ros2/launch/config.yaml
@@ -56,6 +56,13 @@
         cov_warning:  false    # Enable covariance warnings
         nav2_mode:    false    # Enable nav2 mode
 
+        # Optional: omitting this block preserves the legacy WGS-84 LLH output.
+        datum_llh:
+            enabled: false               # Use PROJ to convert the altitude published on odometry_llh and datum
+            ecef_crs: "EPSG:4978"        # Geocentric source CRS of the sensor's ECEF coordinates; normally do not change
+            llh_crs: "EPSG:4979"         # Geographic output CRS. For EGM2008 orthometric height use "EPSG:4326+3855"
+                                         # and install the us_nga_egm08_25.tif PROJ grid. Missing grids are treated as errors.
+
         converter:
             enabled: false
             topic_type: "Twist"        # Supported types: nav_msgs/{Twist, TwistWithCov, Odometry}
diff --git a/fixposition_driver_ros2/src/data_to_ros2.cpp b/fixposition_driver_ros2/src/data_to_ros2.cpp
index e9952743..be0a42c3 100644
--- a/fixposition_driver_ros2/src/data_to_ros2.cpp
+++ b/fixposition_driver_ros2/src/data_to_ros2.cpp
@@ -154,6 +154,9 @@ void PublishFpaOdometryDataImu(const fpa::FpaOdometryPayload& payload, bool nav2
 // ---------------------------------------------------------------------------------------------------------------------
 
 void PublishFpaOdometryDataNavSatFix(const fpa::FpaOdometryPayload& payload, bool nav2_mode_,
+#if FPSDK_USE_PROJ
+                                     const trafo::Transformer* llh_trafo,
+#endif
                                      rclcpp::Publisher<sensor_msgs::msg::NavSatFix>::SharedPtr& pub) {
     if (pub->get_subscription_count() > 0) {
         sensor_msgs::msg::NavSatFix msg;
@@ -174,14 +177,21 @@ void PublishFpaOdometryDataNavSatFix(const fpa::FpaOdometryPayload& payload, boo
             msg.position_covariance_type = msg.COVARIANCE_TYPE_UNKNOWN;
             cov_map = Eigen::Matrix3d::Zero();  // FIXME: necessary?
         } else {
-            const Eigen::Vector3d llh_pos = trafo::TfWgs84LlhEcef(pose.position);
+            Eigen::Vector3d llh_pos;
+#if FPSDK_USE_PROJ
+            if (!EcefToLlhRad(llh_trafo, pose.position, llh_pos)) {
+                return;
+            }
+#else
+            llh_pos = trafo::TfWgs84LlhEcef(pose.position);
+#endif
             msg.latitude = math::RadToDeg(llh_pos(0));
             msg.longitude = math::RadToDeg(llh_pos(1));
             msg.altitude = llh_pos(2);
 
             // Populate LLH covariance
             const Eigen::Matrix3d p_cov_e = pose.cov.topLeftCorner(3, 3);
-            const Eigen::Matrix3d C_l_e = trafo::RotEnuEcef(pose.position);
+            const Eigen::Matrix3d C_l_e = trafo::RotEnuEcef(llh_pos.x(), llh_pos.y());
             const Eigen::Matrix3d p_cov_l = C_l_e * p_cov_e * C_l_e.transpose();
             cov_map = p_cov_l;
             msg.position_covariance_type = msg.COVARIANCE_TYPE_KNOWN;
@@ -885,6 +895,9 @@ void PublishJumpWarning(const JumpDetector& jump_detector, rclcpp::Publisher<fpm
 // ---------------------------------------------------------------------------------------------------------------------
 
 void PublishDatum(const geometry_msgs::msg::Vector3& payload, const builtin_interfaces::msg::Time& stamp,
+#if FPSDK_USE_PROJ
+                  const trafo::Transformer* llh_trafo,
+#endif
                   rclcpp::Publisher<sensor_msgs::msg::NavSatFix>::SharedPtr& pub) {
     if (pub->get_subscription_count() > 0) {
         sensor_msgs::msg::NavSatFix msg;
@@ -893,7 +906,14 @@ void PublishDatum(const geometry_msgs::msg::Vector3& payload, const builtin_inte
 
         // Populate LLH position
         const Eigen::Vector3d position = {payload.x, payload.y, payload.z};
-        const Eigen::Vector3d llh_pos = trafo::TfWgs84LlhEcef(position);
+        Eigen::Vector3d llh_pos;
+#if FPSDK_USE_PROJ
+        if (!EcefToLlhRad(llh_trafo, position, llh_pos)) {
+            return;
+        }
+#else
+        llh_pos = trafo::TfWgs84LlhEcef(position);
+#endif
         msg.latitude = math::RadToDeg(llh_pos(0));
         msg.longitude = math::RadToDeg(llh_pos(1));
         msg.altitude = llh_pos(2);
diff --git a/fixposition_driver_ros2/src/fixposition_driver_node.cpp b/fixposition_driver_ros2/src/fixposition_driver_node.cpp
index 5352e3cf..e94426fe 100644
--- a/fixposition_driver_ros2/src/fixposition_driver_node.cpp
+++ b/fixposition_driver_ros2/src/fixposition_driver_node.cpp
@@ -18,6 +18,7 @@
 #include <functional>
 #include <future>
 #include <memory>
+#include <stdexcept>
 #include <vector>
 
 /* EXTERNAL */
@@ -66,6 +67,20 @@ FixpositionDriverNode::FixpositionDriverNode(std::shared_ptr<rclcpp::Node> nh,
     else if (params_.qos_type_ == "default_long") {
         qos_settings_ = rclcpp::QoS(rclcpp::KeepLast(10), rmw_qos_profile_default);
     }
+
+#if FPSDK_USE_PROJ
+    std::string error;
+    if (!InitLlhTrafo(params_, llh_trafo_, error)) {
+        throw std::runtime_error("Failed initializing PROJ transformation: " + error);
+    }
+    if (llh_trafo_) {
+        RCLCPP_INFO(logger_, "PROJ enabled for ECEF to LLH output conversion");
+    }
+#else
+    if (params_.datum_llh_enabled_) {
+        throw std::runtime_error("Failed initializing PROJ transformation: driver was built without PROJ support");
+    }
+#endif
 }
 
 FixpositionDriverNode::~FixpositionDriverNode() {}
@@ -106,7 +121,11 @@ bool FixpositionDriverNode::StartNode() {
             auto odometry_payload = dynamic_cast<const fpa::FpaOdometryPayload&>(payload);
             PublishFpaOdometry(odometry_payload, fpa_odometry_pub_);
             PublishFpaOdometryDataImu(odometry_payload, params_.nav2_mode_, poiimu_pub_);
+#if FPSDK_USE_PROJ
+            PublishFpaOdometryDataNavSatFix(odometry_payload, params_.nav2_mode_, llh_trafo_.get(), odometry_llh_pub_);
+#else
             PublishFpaOdometryDataNavSatFix(odometry_payload, params_.nav2_mode_, odometry_llh_pub_);
+#endif
             OdometryData odometry_data;
             odometry_data.SetFromFpaOdomPayload(odometry_payload);
             PublishOdometryData(odometry_data, odometry_ecef_pub_);
@@ -736,8 +755,12 @@ void FixpositionDriverNode::PublishNav2Tf() {
     tf_odom_base.transform = tf2::toMsg(tf_ENU0POISH);
     tf_br_->sendTransform(tf_odom_base);
 
-    // Publish WGS84 datum
+    // Publish datum in the configured LLH CRS
+#if FPSDK_USE_PROJ
+    PublishDatum(trans_ecef_enu0, tfs_.enu0_poi_->header.stamp, llh_trafo_.get(), datum_pub_);
+#else
     PublishDatum(trans_ecef_enu0, tfs_.enu0_poi_->header.stamp, datum_pub_);
+#endif
 }
 
 /* ****************************************************************************************************************** */
diff --git a/fixposition_driver_ros2/src/params.cpp b/fixposition_driver_ros2/src/params.cpp
index 1e1298da..7e78992c 100644
--- a/fixposition_driver_ros2/src/params.cpp
+++ b/fixposition_driver_ros2/src/params.cpp
@@ -36,6 +36,9 @@ bool LoadParamsFromRos2(std::shared_ptr<rclcpp::Node>& nh, DriverParams& params)
     const std::string RAW_OUTPUT = "raw_output";
     const std::string COV_WARNING = "cov_warning";
     const std::string NAV2_MODE = "nav2_mode";
+    const std::string DATUM_LLH_ENABLED = "datum_llh.enabled";
+    const std::string DATUM_LLH_ECEF_CRS = "datum_llh.ecef_crs";
+    const std::string DATUM_LLH_LLH_CRS = "datum_llh.llh_crs";
     const std::string CONVERTER_ENABLED = "converter.enabled";
     const std::string CONVERTER_INPUT_TOPIC = "converter.input_topic";
     const std::string CONVERTER_SCALE_FACTOR = "converter.scale_factor";
@@ -58,6 +61,11 @@ bool LoadParamsFromRos2(std::shared_ptr<rclcpp::Node>& nh, DriverParams& params)
     nh->declare_parameter(RAW_OUTPUT, params.raw_output_);
     nh->declare_parameter(COV_WARNING, params.cov_warning_);
     nh->declare_parameter(NAV2_MODE, params.nav2_mode_);
+    // Capture the declared values directly. Parameter overrides are applied by declare_parameter(); when no override
+    // exists, the DriverParams defaults keep configurations created by older releases backward-compatible.
+    params.datum_llh_enabled_ = nh->declare_parameter(DATUM_LLH_ENABLED, params.datum_llh_enabled_);
+    params.datum_llh_ecef_crs_ = nh->declare_parameter(DATUM_LLH_ECEF_CRS, params.datum_llh_ecef_crs_);
+    params.datum_llh_llh_crs_ = nh->declare_parameter(DATUM_LLH_LLH_CRS, params.datum_llh_llh_crs_);
     nh->declare_parameter(CONVERTER_ENABLED, params.converter_enabled_);
     nh->declare_parameter(CONVERTER_INPUT_TOPIC, params.converter_input_topic_);
     nh->declare_parameter(CONVERTER_SCALE_FACTOR, params.converter_scale_factor_);
@@ -178,6 +186,9 @@ bool LoadParamsFromRos2(std::shared_ptr<rclcpp::Node>& nh, DriverParams& params)
     RCLCPP_INFO(logger, "DriverParams: raw_output=%s", params.raw_output_ ? "true" : "false");
     RCLCPP_INFO(logger, "DriverParams: cov_warning=%s", params.cov_warning_ ? "true" : "false");
     RCLCPP_INFO(logger, "DriverParams: nav2_mode=%s", params.nav2_mode_ ? "true" : "false");
+    RCLCPP_INFO(logger, "DriverParams: datum_llh_enabled=%s", params.datum_llh_enabled_ ? "true" : "false");
+    RCLCPP_INFO(logger, "DriverParams: datum_llh_ecef_crs=%s", params.datum_llh_ecef_crs_.c_str());
+    RCLCPP_INFO(logger, "DriverParams: datum_llh_llh_crs=%s", params.datum_llh_llh_crs_.c_str());
     RCLCPP_INFO(logger, "DriverParams: converter_enabled=%s", params.converter_enabled_ ? "true" : "false");
     RCLCPP_INFO(logger, "DriverParams: converter_topic_type=%s", topic_type_string_.c_str());
     RCLCPP_INFO(logger, "DriverParams: converter_input_topic=%s", params.converter_input_topic_.c_str());