Add rail layer

data.yml

@@ -78,6 +78,29 @@ Layer:
     properties: 
       "buffer-size": 4
     srs: +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over
+  - id: rail
+    Datasource: 
+      dbname: osm
+      extent: -20037508.34,-20037508.34,20037508.34,20037508.34
+      geometry_field: geom
+      geometry_table: ''
+      host: db
+      key_field: ''
+      key_field_as_attribute: ''
+      max_size: 512
+      password: osm
+      port: 5432
+      srid: 900913
+      table: (SELECT * FROM layer_rail(!bbox!, z(!scale_denominator!))) AS t
+      type: postgis
+      user: osm
+    description: Buildings
+    fields: 
+      brunnel: String
+      class: String
+    properties: 
+      "buffer-size": 4
+    srs: +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over
   - id: ice
     Datasource: 
       dbname: osm

schema/create_schema.sh

@@ -25,6 +25,7 @@ function main() {
     exec_psql_file "layers/place.sql"
     exec_psql_file "layers/country.sql"
     exec_psql_file "layers/state.sql"
+    exec_psql_file "layers/rail.sql"
 }
 
 main

schema/layers/rail.sql

@@ -0,0 +1,18 @@
+CREATE OR REPLACE VIEW rail_z13 AS (
+    SELECT * FROM rail
+    WHERE class='rail'
+);
+
+CREATE OR REPLACE VIEW rail_z14 AS (
+    SELECT * FROM rail
+);
+
+CREATE OR REPLACE FUNCTION layer_rail(bbox geometry, zoom_level int)
+RETURNS TABLE(geom geometry, class text, brunnel text) AS $$
+    SELECT way AS geom, class::text, brunnel::text FROM (
+        SELECT * FROM rail_z13 WHERE zoom_level = 13
+        UNION ALL
+        SELECT * FROM rail_z14 WHERE zoom_level >= 14
+    ) AS zoom_levels
+    WHERE way && bbox;
+$$ LANGUAGE SQL IMMUTABLE;