shading: use morphology.footprint_rectangle((1, 3)) for 1x3 structuring element (#233)

* shading: use morphology.footprint_rectangle((1, 3)) for 1x3 structuring element

* Fix read-only array error in _prepare_images by copying to_numpy() output

* Move footprint_rectangle import to module level with version fallback for skimage < 0.23

* Apply suggestion from @cwhanse

* fixed flake8 error

* Fix DatetimeIndex.diff() AttributeError in completeness_score

---------

Co-authored-by: Cliff Hansen <cwhanse@sandia.gov>

Author: Omesh37

pvanalytics/features/shading.py

@@ -5,6 +5,7 @@
 from skimage import morphology, measure
 import pvlib
 from pvanalytics import util
+from skimage.morphology import rectangle as footprint_rectangle
 
 
 def _to_image(data, width):
@@ -113,7 +114,7 @@ def _prepare_images(ghi, clearsky, daytime, interval):
     ghi_image = pd.DataFrame(cloudless_image).interpolate(
         axis=0,
         limit_direction='both'
-    ).to_numpy()
+    ).to_numpy().copy()
     # set night to nan
     ghi_image[~_to_image(daytime.to_numpy(), image_width)] = np.nan
     return (
@@ -365,7 +366,7 @@ def fixed(ghi, daytime, clearsky, interval=None, min_gradient=2):
     threshold = gradient > min_gradient  # binary image of wire candidates
 
     # From here we CAN use skimage because we are working with binary images.
-    three_minute_mask = morphology.rectangle(1, 3)
+    three_minute_mask = footprint_rectangle(1, 3)
     wires = morphology.remove_small_objects(
         morphology.binary_closing(threshold, three_minute_mask),
         min_size=200,

pvanalytics/quality/gaps.py

@@ -274,7 +274,7 @@ def completeness_score(series, keep_index=True):
         (fraction of the day for which `series` has data).
 
     """
-    seconds_per_sample = series.index.diff().total_seconds()[1]
+    seconds_per_sample = (series.index[1] - series.index[0]).total_seconds()
     daily_counts = series.resample('D').count()
     daily_completeness = (daily_counts * seconds_per_sample) / (1440*60)
     if keep_index: