diff --git a/HydroGrid.py b/HydroGrid.py
index 3327490e137d667b201cb0efdcf1a76838e65131..8a108c2e8617efeb19de14c344f849675382941d 100644
--- a/HydroGrid.py
+++ b/HydroGrid.py
@@ -33,8 +33,8 @@ def corners(lon, lat) :
     cornerspoly = []
     cornersll = []
     index = []
-    hdlon=(np.max(lon[0,:])-np.min(lon[0,:]))/iim/2.0
-    hdlat=(np.max(lat[:,0])-np.min(lat[:,0]))/jjm/2.0
+    hdlon=np.mean(np.abs(np.diff(lon[0,:])))/2.0
+    hdlat=np.mean(np.abs(np.diff(lat[:,0])))/2.0
     #
     for i in range(iim) :
         for j in range(jjm) :