diff --git a/lib/controls/geoid_grid.dart b/lib/controls/geoid_grid.dart
new file mode 100644
index 0000000..6317fb3
--- /dev/null
+++ b/lib/controls/geoid_grid.dart
@@ -0,0 +1,67 @@
+import 'dart:typed_data';
+import 'package:flutter/services.dart';
+
+class GeoidGrid {
+  final double southLat, westLon, latStep, lonStep;
+  final int nRows, nCols;
+  final Float32List grid; // big-endian, south-to-north
+
+  GeoidGrid._(this.southLat, this.westLon, this.latStep, this.lonStep,
+      this.nRows, this.nCols, this.grid);
+
+  static Future<GeoidGrid> load(String assetPath) async {
+    final bytes = (await rootBundle.load(assetPath)).buffer.asByteData();
+    final southLat = bytes.getFloat64(0, Endian.big);
+    final westLon = bytes.getFloat64(8, Endian.big);
+    final latStep = bytes.getFloat64(16, Endian.big);
+    final lonStep = bytes.getFloat64(24, Endian.big);
+    final nRows = bytes.getInt32(32, Endian.big);
+    final nCols = bytes.getInt32(36, Endian.big);
+
+    final grid = Float32List(nRows * nCols);
+    for (int i = 0; i < grid.length; i++) {
+      grid[i] = bytes.getFloat32(40 + i * 4, Endian.big);
+    }
+    return GeoidGrid._(southLat, westLon, latStep, lonStep, nRows, nCols, grid);
+  }
+
+  /// Returns EHT2014 geoid undulation [m] at (lat, lon) via bilinear interpolation.
+  /// Returns null if outside grid or in no-data area.
+  double? getUndulation(double lat, double lon) {
+    final rowF = (lat - southLat) / latStep;
+    final colF = (lon - westLon) / lonStep;
+    final r0 = rowF.floor();
+    final c0 = colF.floor();
+    if (r0 < 0 || r0 >= nRows - 1 || c0 < 0 || c0 >= nCols - 1) return null;
+
+    final dr = rowF - r0;
+    final dc = colF - c0;
+
+    double v(int r, int c) => grid[r * nCols + c].toDouble();
+    final noData = -80.0;
+    final v00 = v(r0, c0);
+    if (v00 < noData) return null;
+    final v10 = v(r0 + 1, c0);
+    if (v10 < noData) return null;
+    final v01 = v(r0, c0 + 1);
+    if (v01 < noData) return null;
+    final v11 = v(r0 + 1, c0 + 1);
+    if (v11 < noData) return null;
+
+    return v00 * (1 - dr) * (1 - dc) +
+        v10 * dr * (1 - dc) +
+        v01 * (1 - dr) * dc +
+        v11 * dr * dc;
+  }
+
+  /// Orthometric height in the Hungarian EHT2014 system.
+  /// [nmea_ortho] = GGA field 9 (altitudeAboveMeanSeaLevel)
+  /// [nmea_sep]   = GGA field 11 (geoidSeparation from receiver)
+  double? toEovHeight(
+      double lat, double lon, double nmeaOrtho, double nmeaSep) {
+    final nEht2014 = getUndulation(lat, lon);
+    if (nEht2014 == null) return null;
+    final ellipsoidal = nmeaOrtho + nmeaSep; // h = H + N_receiver
+    return ellipsoidal - nEht2014; // H_EOV = h - N_EHT2014
+  }
+}
diff --git a/lib/pages/map/presentation/controllers/map_controller.dart b/lib/pages/map/presentation/controllers/map_controller.dart
index acfdd60..5932306 100644
--- a/lib/pages/map/presentation/controllers/map_controller.dart
+++ b/lib/pages/map/presentation/controllers/map_controller.dart
@@ -21,6 +21,7 @@ import 'package:permission_handler/permission_handler.dart'
     as permission_handler;
 import 'package:share_plus/share_plus.dart';
 import 'package:supabase_flutter/supabase_flutter.dart';
+import 'package:terepi_seged/controls/geoid_grid.dart';
 import 'package:terepi_seged/eov/convert_coordinate.dart';
 import 'package:terepi_seged/eov/eov.dart';
 import 'package:terepi_seged/gnss_sentences/gngga.dart';
@@ -78,6 +79,8 @@ class MapViewController extends GetxController {
   RxDouble gpsAltitudeError = 0.0.obs;
   Rx<DateTime> gpsDateTime = DateTime(2000).obs;
   Rx<Eov> eov = Eov(0, 0).obs;
+  Rx<double?> eovHeight = 0.0.obs;
+
   RxInt latDegree = 0.obs;
   RxInt latMin = 0.obs;
   RxDouble latSec = 0.0.obs;
@@ -99,6 +102,8 @@ class MapViewController extends GetxController {
   RxInt pointsToMeasureSelectedValue = (-1).obs;
   RxDouble distance = 0.0.obs;
 
+  late GeoidGrid geoidGrid;
+
   TextEditingController pointIdController = TextEditingController();
   TextEditingController pointDescriptionController = TextEditingController();
   TextEditingController gpsHeightController = TextEditingController();
@@ -180,6 +185,8 @@ class MapViewController extends GetxController {
             })
         .subscribe();
 
+    geoidGrid = await GeoidGrid.load('assets/Grids/geoid_eht2014.gtx');
+
     mapController = MapController();
 
     // riveGpsIconController = RiveUtils.getRiveController(Artboard(),
@@ -482,6 +489,11 @@ class MapViewController extends GetxController {
               gpsQuality.value = sentence.gpsQualityIndicator;
               eov.value = ConvertCoordinate.ConvertWgsToEov(
                   gpsLatitude.value, gpsLongitude.value);
+              eovHeight.value = geoidGrid?.toEovHeight(
+                  gpsLatitude.value,
+                  gpsLongitude.value,
+                  gpsAltitude.value,
+                  gpsGeoidSeparation.value);
 
               if (pointsToMeasureSelectedValue.value >= 0) {
                 double coordX =
diff --git a/lib/pages/map/presentation/views/map_view.dart b/lib/pages/map/presentation/views/map_view.dart
index 33d1fd5..295b8b9 100644
--- a/lib/pages/map/presentation/views/map_view.dart
+++ b/lib/pages/map/presentation/views/map_view.dart
@@ -154,7 +154,7 @@ class MapView extends GetView<MapViewController> {
                                     "EovX: ${controller.formatEov.format(controller.eov.value.Y)}"),
                                 Text(
                                     "EovY: ${controller.formatEov.format(controller.eov.value.X)}"),
-                                Text("Alt: ${controller.gpsAltitude} (m)"),
+                                Text("Alt: ${controller.eovHeight.value} (m)"),
                                 const Divider(
                                   height: 5.0,
                                   color: Colors.black,