Improve heightmap export stability

export_heightmaps.py

@@ -23,8 +23,8 @@ if ds is None:
 
 band = ds.GetRasterBand(1)
 
-# Strategy B: compute global min/max for CURRENT downloaded AOI
-gmin, gmax = band.ComputeRasterMinMax(True)
+# Strategy B: compute global min/max for CURRENT downloaded AOI (full scan for stability)
+gmin, gmax = band.ComputeRasterMinMax(False)
 print(f"GLOBAL_MIN={gmin}, GLOBAL_MAX={gmax}")
 
 # Export manifest for Unity placement later
@@ -59,7 +59,8 @@ with open(manifest_path, "w", encoding="utf-8") as f:
             width=OUT_RES,
             height=OUT_RES,
             resampleAlg=RESAMPLE,
-            dstNodata=-9999,
+            srcNodata=-9999,
+            dstNodata=gmin,  # fill nodata with global min to avoid deep pits
         )
         gdal.Warp(tmp_path, ds, options=warp_opts)