Feature/update Collection extent from Items

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [v0.5.2]
+
+### Added 
+
+- `update_extent_from_items` method to Collection for updating Extent objects within a collection based on the contained items. ([#168](https://github.com/stac-utils/pystac/pull/168)) 
+
 ## [v0.5.1]
 
 ### Added

pystac/collection.py

@@ -1,7 +1,7 @@
 from datetime import datetime
 import dateutil.parser
+from dateutil import tz
 from copy import (copy, deepcopy)
-
 from pystac import (STACError, STACObjectType)
 from pystac.catalog import Catalog
 from pystac.link import Link
@@ -202,6 +202,37 @@ def from_dict(cls, d, href=None, root=None):
 
         return collection
 
+    def update_extent_from_items(self):
+        """
+        Update datetime and bbox based on all items to a single bbox and time window.
+        """
+        def extract_extent_props(item):
+            return item.bbox + [
+                item.datetime, item.common_metadata.start_datetime,
+                item.common_metadata.end_datetime
+            ]
+
+        xmins, ymins, xmaxs, ymaxs, datetimes, starts, ends = zip(
+            *map(extract_extent_props, self.get_all_items()))
+
+        if not any(datetimes + starts):
+            start_timestamp = None
+        else:
+            start_timestamp = min([
+                dt if dt.tzinfo else dt.replace(tzinfo=tz.UTC)
+                for dt in filter(None, datetimes + starts)
+            ])
+        if not any(datetimes + ends):
+            end_timestamp = None
+        else:
+            end_timestamp = max([
+                dt if dt.tzinfo else dt.replace(tzinfo=tz.UTC)
+                for dt in filter(None, datetimes + ends)
+            ])
+
+        self.extent.spatial.bboxes = [[min(xmins), min(ymins), max(xmaxs), max(ymaxs)]]
+        self.extent.temporal.intervals = [[start_timestamp, end_timestamp]]
+
 
 class Extent:
     """Describes the spatio-temporal extents of a Collection.

tests/test_collection.py

@@ -9,6 +9,7 @@
 from pystac.serialization.identify import STACObjectType
 from pystac import (Collection, Item, Extent, SpatialExtent, TemporalExtent, CatalogType)
 from pystac.extensions.eo import Band
+from pystac.utils import datetime_to_str
 from tests.utils import (TestCases, RANDOM_GEOM, RANDOM_BBOX)
 
 
@@ -135,3 +136,46 @@ def test_extra_fields(self):
             read_col = pystac.read_file(p)
             self.assertTrue('test' in read_col.extra_fields)
             self.assertEqual(read_col.extra_fields['test'], 'extra')
+
+    def test_update_extents(self):
+
+        catalog = TestCases.test_case_2()
+        base_collection = catalog.get_child('1a8c1632-fa91-4a62-b33e-3a87c2ebdf16')
+        base_extent = base_collection.extent
+        collection = base_collection.clone()
+
+        item1 = Item(id='test-item-1',
+                     geometry=RANDOM_GEOM,
+                     bbox=[-180, -90, 180, 90],
+                     datetime=datetime.utcnow(),
+                     properties={'key': 'one'},
+                     stac_extensions=['eo', 'commons'])
+
+        item2 = Item(id='test-item-1',
+                     geometry=RANDOM_GEOM,
+                     bbox=[-180, -90, 180, 90],
+                     datetime=None,
+                     properties={
+                         'start_datetime': datetime_to_str(datetime(2000, 1, 1, 12, 0, 0, 0)),
+                         'end_datetime': datetime_to_str(datetime(2000, 2, 1, 12, 0, 0, 0))
+                     },
+                     stac_extensions=['eo', 'commons'])
+
+        collection.add_item(item1)
+
+        collection.update_extent_from_items()
+        self.assertEqual([[-180, -90, 180, 90]], collection.extent.spatial.bboxes)
+        self.assertEqual(len(base_extent.spatial.bboxes[0]),
+                         len(collection.extent.spatial.bboxes[0]))
+
+        self.assertNotEqual(base_extent.temporal.intervals, collection.extent.temporal.intervals)
+        collection.remove_item('test-item-1')
+        collection.update_extent_from_items()
+        self.assertNotEqual([[-180, -90, 180, 90]], collection.extent.spatial.bboxes)
+        collection.add_item(item2)
+
+        collection.update_extent_from_items()
+
+        self.assertEqual(
+            [[item2.common_metadata.start_datetime, base_extent.temporal.intervals[0][1]]],
+            collection.extent.temporal.intervals)