Fix alert tagging issue with circle geo data (#117)

* Fix typo
* Convert km to degree for filter by circle
* Fix circular dependency

apps/cap_feed/formats/cap_xml.py

@@ -27,6 +27,7 @@
     Feed,
     ProcessedAlert,
 )
+from apps.cap_feed.utils import distance_to_decimal_degrees
 from main.managers import BulkCreateManager
 
 logger = logging.getLogger(__name__)
@@ -251,7 +252,13 @@ def process_alert(
             for circle in alert_info_circles_collections:
                 possible_admin1s = admin1_base_qs.filter(
                     # TODO: Check for performance issues
-                    geometry___dwithin=(circle[0], Distance(m=circle[1])),
+                    geometry__dwithin=(
+                        circle[0],
+                        distance_to_decimal_degrees(
+                            Distance(km=circle[1]),
+                            circle[0],
+                        ),
+                    ),
                 ).exclude(id__in=tagged_admin1s_id)
                 for admin1_id in possible_admin1s.values_list('id', flat=True):
                     tagged_admin1s_id.add(admin1_id)

apps/cap_feed/utils.py

@@ -1,13 +1,15 @@
 import json
 import logging
+import math
 
+from django.contrib.gis.geos import Point
+from django.contrib.gis.measure import Distance
 from django.utils import timezone
 from django_celery_beat.models import IntervalSchedule, PeriodicTask
 
 from main.celery import INTERNAL_CELERY_TASK_NAME_PREFIX
 
 from .models import Feed
-from .tasks import poll_feed
 
 logger = logging.getLogger(__name__)
 
@@ -35,6 +37,9 @@ def force_delete_all_tasks(cls):
 
     @classmethod
     def add_task(cls, feed: Feed):
+        # XXX: Circular dependency fix
+        from .tasks import poll_feed
+
         interval_schedule, _ = IntervalSchedule.objects.get_or_create(
             every=feed.polling_interval,
             period='seconds',
@@ -64,3 +69,10 @@ def remove_task(cls, feed: Feed):
     def update_task(cls, feed: Feed):
         cls.remove_task(feed)
         cls.add_task(feed)
+
+
+def distance_to_decimal_degrees(distance: Distance, point: Point):
+    # https://gis.stackexchange.com/a/384823
+    lat_radians = point.y * (math.pi / 180)  # Where point.y is latitude
+    # 1 longitudinal degree at the equator equal 111,319.5m equiv to 111.32km
+    return distance.m / (111_319.5 * math.cos(lat_radians))