add state name to national borders (#1039)

This PR adds state name to national borders (`admin_level=2`)

From zoom level 3 there is an added `adm0_l` and `adm0_r` attribute for national borders.

There is 3 main steps: 
1) union border lines from OSM and keep separate LineString between intersects
2) create polygons from step 1), create a point in each state polygon, add to this point a state abbreviation from NaturalEarth Data
3) create a short parallel line on the left and right of a small part of the border in 70m distance, and add information about which state overlap this short line.

layers/boundary/boundary_name.sql

@@ -0,0 +1,99 @@
+DROP TABLE IF EXISTS osm_border_linestring_adm CASCADE;
+
+-- etldoc: osm_border_linestring -> osm_border_linestring_adm
+CREATE TABLE IF NOT EXISTS osm_border_linestring_adm AS ( 
+  WITH 
+    -- Prepare lines from osm to be merged
+	multiline AS (
+    	SELECT ST_Node(ST_Collect(geometry)) AS geometry, 
+			   maritime,
+			   disputed
+    	FROM osm_border_linestring
+    	WHERE admin_level = 2
+		    AND osm_id NOT IN (SELECT DISTINCT osm_id FROM osm_border_disp_linestring)
+		GROUP BY maritime,
+				 disputed
+		),
+
+	mergedline AS (
+		SELECT (ST_Dump(
+      		     ST_LineMerge(geometry))).geom AS geometry,
+			maritime,
+			disputed
+  		FROM multiline
+		),
+    -- Create polygons from all boundaries to preserve real shape of country
+	polyg AS (
+    	SELECT (ST_Dump(
+        		 ST_Polygonize(geometry))).geom AS geometry  
+    	FROM (
+			SELECT (ST_Dump(
+      				ST_LineMerge(geometry))).geom AS geometry
+  			FROM (SELECT ST_Node(
+                          ST_Collect(geometry)) AS geometry
+    			FROM osm_border_linestring
+    			WHERE admin_level = 2
+                ) nodes
+			) linemerge
+  		), 
+
+    centroids AS (
+		SELECT polyg.geometry,
+			   ne.adm0_a3
+		FROM polyg,
+			 ne_10m_admin_0_countries AS ne
+		WHERE ST_Within(
+			   ST_PointOnSurface(polyg.geometry), ne.geometry)
+    	),
+
+	country_osm_polyg AS  (
+		SELECT country.adm0_a3,
+			   border.geometry
+  		FROM polyg border,
+			 centroids country
+  		WHERE ST_Within(country.geometry, border.geometry)
+	),
+
+	rights AS (
+    	SELECT adm0_r,
+			   geometry,
+			   maritime,
+			   disputed
+		FROM (
+			SELECT b.adm0_a3 AS adm0_r,
+                   a.geometry,
+                   a.maritime,
+                   a.disputed
+			FROM mergedline AS a
+			LEFT JOIN country_osm_polyg AS b
+            -- Create short line on the right of the boundary (mergedline) and find state where line lies.
+			ON ST_Within(
+				ST_OffsetCurve(
+				(ST_LineSubString(a.geometry, 0.3,0.3004)), 70, 'quad_segs=4 join=mitre'), b.geometry)
+            ) line_rights
+		)
+
+  SELECT adm0_l,
+		 adm0_r,
+		 geometry,
+		 maritime,
+		 2::integer AS admin_level,
+		 disputed
+  FROM (
+    SELECT b.adm0_a3 AS adm0_l,
+           r.adm0_r AS adm0_r,
+           r.geometry,
+           r.maritime,
+           r.disputed
+    FROM rights AS r
+    LEFT JOIN country_osm_polyg AS b
+      -- Create short line on the left of the boundary (mergedline) and find state where line lies.
+      ON ST_Within(
+        ST_OffsetCurve(
+          (ST_LineSubString(r.geometry, 0.4,0.4004)), -70, 'quad_segs=4 join=mitre'), b.geometry)
+    ) both_lines
+);
+
+CREATE INDEX IF NOT EXISTS osm_border_linestring_adm_geom_idx
+  ON osm_border_linestring_adm
+  USING GIST (geometry);