Move railway over to imposm3 and improve z_order

layers/railway/mapping.yaml

@@ -0,0 +1,33 @@
+tables:
+  railway_linestring:
+    type: linestring
+    fields:
+    - name: osm_id
+      type: id
+    - name: geometry
+      type: geometry
+    - key: railway
+      name: railway
+      type: string
+    - name: z_order
+      type: wayzorder
+    - key: tunnel
+      name: is_tunnel
+      type: bool
+    - key: bridge
+      name: is_bridge
+      type: bool
+    - key: service
+      name: service
+      type: string
+    - key: usage
+      name: usage
+      type: string
+    mapping:
+      railway:
+      - rail
+      - light_rail
+      - subway
+      - narrow_gauge
+      - preserved
+      - tram

layers/railway/railway.sql

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+CREATE OR REPLACE FUNCTION railway_class(railway text, service text) RETURNS TEXT AS $$
+    SELECT CASE
+        WHEN railway='rail' AND service='' THEN 'rail'
+        ELSE 'minor'
+    END;
+$$ LANGUAGE SQL IMMUTABLE;
+
+CREATE OR REPLACE FUNCTION railway_brunnel(is_bridge boolean, is_tunnel boolean) RETURNS TEXT AS $$
+    SELECT CASE
+         WHEN is_bridge THEN 'bridge'
+         WHEN is_tunnel THEN 'tunnel'
+        ELSE NULL
+    END;
+$$ LANGUAGE SQL IMMUTABLE;
+
+CREATE OR REPLACE VIEW railway_z13 AS (
+    SELECT * FROM osm_railway_linestring
+    WHERE railway = 'rail' AND service=''
+);
+
+CREATE OR REPLACE VIEW railway_z14 AS (
+    SELECT * FROM osm_railway_linestring
+);
+
+CREATE OR REPLACE FUNCTION layer_railway(bbox geometry, zoom_level int)
+RETURNS TABLE(geometry geometry, class text, subclass text, brunnel text) AS $$
+    SELECT geometry,
+        railway_class(railway, service) AS class,
+        railway AS subclass,
+        railway_brunnel(is_bridge, is_tunnel) AS brunnel
+    FROM (
+        SELECT * FROM railway_z13 WHERE zoom_level = 13
+        UNION ALL
+        SELECT * FROM railway_z14 WHERE zoom_level >= 14
+    ) AS zoom_levels
+    WHERE geometry && bbox
+    ORDER BY z_order ASC;
+$$ LANGUAGE SQL IMMUTABLE;

layers/railway/railway.yaml

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+layer:
+  id: "railway"
+  description: Rail
+  buffer_size: 4
+  datasource:
+    geometry_field: geometry
+    query: (SELECT * FROM layer_railway(!bbox!, z(!scale_denominator!))) AS t
+schema:
+  - ./railway.sql
+datasources:
+  - type: imposm3
+    mapping_file: ./mapping.yaml