--- a/schema/auth.sql	Mon Nov 19 18:32:06 2018 +0100
+++ b/schema/auth.sql	Tue Nov 20 00:51:33 2018 +0100
@@ -89,15 +89,49 @@
 -- RLS policies for waterway_admin
 --
 
+CREATE OR REPLACE FUNCTION best_utm(g geometry) RETURNS integer AS
+$$
+DECLARE
+  center geometry;
+BEGIN
+  SELECT ST_Centroid(g) INTO center;
+  RETURN
+    CASE WHEN ST_Y(center) > 0 THEN
+    32600
+  ELSE
+    32700
+  END + floor((ST_X(center)+180)/6)::int + 1;
+END;
+$$
+LANGUAGE plpgsql
+IMMUTABLE;
+
+CREATE OR REPLACE FUNCTION utm_covers(g geography) RETURNS boolean AS
+$$
+DECLARE
+  user_area geometry;
+  utm integer;
+BEGIN
+    SELECT area::geometry FROM users.responsibility_areas INTO user_area
+    WHERE country = users.current_user_country();
+    SELECT best_utm(user_area) INTO utm;
+    RETURN ST_Covers(
+      ST_Transform(user_area, utm),
+      ST_Transform(g::geometry, utm));
+END;
+$$
+LANGUAGE plpgsql
+STABLE;
+
 -- Staging area
 -- TODO: add all relevant tables here
+
 CREATE POLICY responsibility_area ON waterway.bottlenecks
     FOR ALL TO waterway_admin
-    USING (ST_CoveredBy(area, (SELECT area FROM users.responsibility_areas
-        WHERE country = users.current_user_country())));
+    USING (utm_covers(area));
+
 CREATE POLICY responsibility_area ON waterway.sounding_results
     FOR ALL TO waterway_admin
-    USING (ST_CoveredBy(area, (SELECT area FROM users.responsibility_areas
-        WHERE country = users.current_user_country())));
+    USING (utm_covers(area));
 
 COMMIT;