Add method to get box slices

lib/box.py

@@ -89,8 +89,8 @@ class Box:
         sh = box(*self.corner_ll, *self.corner_ur)
         return sh
 
-    def extract(self, ds, enlarge=False):
-        """Return dataset (or array) inside box.
+    def get_isel(self, ds, enlarge=False):
+        """Return slices indices to select box in Xarray object.
 
         Parameters:
         -----------
@@ -126,7 +126,18 @@ class Box:
 
         enlarge_slice(slice_lon, slice_lat, enlarge)
 
-        return ds.isel(lon=slice(*slice_lon), lat=slice(*slice_lat))
+        return dict(lon=slice(*slice_lon), lat=slice(*slice_lat))
+
+    def extract(self, ds, enlarge=False):
+        """Return dataset (or array) inside box.
+
+        Parameters:
+        -----------
+        enlarge:
+            Expends the area by a number of pixel on each side.
+            If is True, enlarge by 2 pixels by default.
+        """
+        return ds.isel(**self.get_isel(ds, enlarge))
 
     def add_to_plot(self, ax, **kwargs):
         """Plot area on axis.