better vdatum/fes blending; blend inland from final instead of vdatum only

Author: matth-love

src/transformez/grid_engine.py

@@ -190,6 +190,10 @@ def smart_blend(in_grid, background_grid, blend_pixels=50):
         dist = ndimage.distance_transform_edt(mask)
         alpha = np.clip(dist / blend_pixels, 0.0, 1.0)
 
+        # --- Hermite Interpolation ---
+        # This converts the linear gradient into a smooth S-curve
+        alpha = alpha * alpha * (3.0 - 2.0 * alpha)
+
         nearest_indices = ndimage.distance_transform_edt(
             mask, return_distances=False, return_indices=True
         )
@@ -210,6 +214,7 @@ def coastal_aware_composite(
         shapefiles=None,
         decay_pixels=100,
         buffer_pixels=10,
+        blend_pixels=50,
     ):
         """Handles inland decay vs. offshore blending, while
         filtering out low-resolution global artifacts.
@@ -230,14 +235,13 @@ def coastal_aware_composite(
 
         if is_offshore.any():
             blended_ocean = GridEngine.smart_blend(
-                vdatum_grid, global_grid, blend_pixels=50
+                vdatum_grid, global_grid, blend_pixels=blend_pixels
             )
             final_grid[is_offshore] = blended_ocean[is_offshore]
 
         if is_inland.any():
-            source_for_decay = vdatum_grid if is_vdatum.any() else final_grid
             decayed_inland = GridEngine.fill_nans(
-                source_for_decay,
+                final_grid,
                 decay_pixels=decay_pixels,
                 buffer_pixels=buffer_pixels,
                 land_mask=land_mask,