diff --git a/api/app/core/viewshed.py b/api/app/core/viewshed.py
index 6bcbd21..7e7eff9 100644
--- a/api/app/core/viewshed.py
+++ b/api/app/core/viewshed.py
@@ -98,6 +98,7 @@ def _run_gdal_viewshed(
     observer_y: float,
     observer_height: float,
     target_height: float,
+    max_distance: float,
     output_path: Path,
     gdal_bin: str,
 ) -> None:
@@ -111,6 +112,8 @@ def _run_gdal_viewshed(
         str(observer_height),
         "-tz",
         str(target_height),
+        "-md",
+        str(max_distance),
         "-vv",
         "255",
         "-iv",
@@ -199,19 +202,13 @@ def compute_viewshed(
             request.radius_m,
             metric_dem,
         )
-        with rasterio.open(source_tile) as source_dataset:
-            observer_elevation = _sample_dataset(
-                source_dataset,
-                observer.lat,
-                observer.lon,
-            )
-        observer_abs = float(observer_elevation or 0.0) + request.observer.height_agl
         _run_gdal_viewshed(
             metric_path,
             observer_x,
             observer_y,
-            observer_abs,
+            request.observer.height_agl,
             request.target_height_agl,
+            request.radius_m,
             viewshed_raster,
             gdal_viewshed_bin,
         )