diff --git a/03_nc_to_npy_for_openvdb.py b/03_nc_to_npy_for_openvdb.py
index 9c21100..fcba4e3 100644
--- a/03_nc_to_npy_for_openvdb.py
+++ b/03_nc_to_npy_for_openvdb.py
@@ -50,12 +50,12 @@ def str2bool(v):
     else:
         raise argparse.ArgumentTypeError('Boolean value expected.')
 
-def find_free_GPU_memory(gpu_id):
+def find_free_GPU_memory(gpu_id, limit=0.5):
     free = cp.cuda.Device(gpu_id).mem_info[0]/cp.cuda.Device(gpu_id).mem_info[1]
     
-    while free<0.25:
+    while free<limit:
         gpu_id = (gpu_id+1)%num_GPU #for all available GPUs
-        sleep(1)
+        sleep(2)
         free = cp.cuda.Device(gpu_id).mem_info[0]/cp.cuda.Device(gpu_id).mem_info[1]
         
     return gpu_id
diff --git a/04_npy_to_openvdb_in_blender.py b/04_npy_to_openvdb_in_blender.py
index c835829..799b7e9 100644
--- a/04_npy_to_openvdb_in_blender.py
+++ b/04_npy_to_openvdb_in_blender.py
@@ -48,6 +48,11 @@ def check_npy_folder(toppath):
 
 def convert_npy_to_vdb(file,toppath, topoutpath, x1,x2,y1,y2,z1,z2):
     im = np.load(os.path.join(toppath,file))
+    
+    # special crop for sample 4 GDL
+    im[:,:170,:] = False
+    im[:,:,:230] = False
+    
     imc = im[x1:x2,y1:y2,z1:z2]
     
     # im1 = imc == 0