Changing C2 scaling to not clip to 0, and use nodata instead (#48)

* changing c2 scaling to not clip to 0, and use nodata instead

* addition of upper valid range

* tidying the valid min and max

* <= and >= for the min and max

wofs/virtualproduct.py

@@ -20,11 +20,12 @@
 def scale_usgs_collection2(data):
     """These are taken from the Fractional Cover scaling values"""
     return data.apply(scale_and_clip_dataarray, keep_attrs=True,
-                      scale_factor=0.275, add_offset=-2000, clip_range=(0, 10000))
+                      scale_factor=0.275, add_offset=-2000, 
+                      clip_range=None, valid_range=(0, 10000))
 
 
 def scale_and_clip_dataarray(dataarray: xr.DataArray, *, scale_factor=1, add_offset=0, clip_range=None,
-                             new_nodata=-999, new_dtype='int16'):
+                             valid_range=None, new_nodata=-999, new_dtype='int16'):
     orig_attrs = dataarray.attrs
     nodata = dataarray.attrs['nodata']
 
@@ -40,6 +41,10 @@ def scale_and_clip_dataarray(dataarray: xr.DataArray, *, scale_factor=1, add_off
     dataarray = dataarray.astype(new_dtype)
 
     dataarray.data[mask] = new_nodata
+    if valid_range is not None:
+        valid_min, valid_max = valid_range
+        dataarray = dataarray.where(dataarray>= valid_min, new_nodata)
+        dataarray = dataarray.where(dataarray<= valid_max, new_nodata)
     dataarray.attrs = orig_attrs
     dataarray.attrs['nodata'] = new_nodata