Add building heights (#56)

* Add better support for 3d buildings

Change key from "levels" to "building:levels" as the "levels" key is non-standard and sees much less use than "building:levels"

* Fix typo in sql definition and missing render_min_height

* Add render_height and min_height to building.yaml

* Simplify the render, switch numeric to int.

Assume min_height cannot be negative. There are a few examples in overpass, but can't show below ground anyways in mapbox (https://github.com/mapbox/mapbox-gl-js/issues/3456). Also don't attempt to fix min_height>height

* Remove colour as it is not currently used

layers/building/building.sql

@@ -5,17 +5,18 @@
 -- etldoc:     label="layer_building | <z13> z13 | <z14_> z14_ " ] ;
 
 CREATE OR REPLACE FUNCTION layer_building(bbox geometry, zoom_level int)
-RETURNS TABLE(geom geometry, osm_id bigint, render_height numeric) AS $$
+RETURNS TABLE(geom geometry, osm_id bigint, render_height int, render_min_height int) AS $$
     SELECT geometry, osm_id,
-    least(greatest(3, COALESCE(height, levels*3.66,5)),400)^.7::int AS render_height
+    greatest(5, COALESCE(height, levels*3.66,5))::int AS render_height,
+    greatest(0, COALESCE(min_height, min_level*3.66,0))::int AS render_min_height
     FROM (
 
         -- etldoc: osm_building_polygon_gen1 -> layer_building:z13
-        SELECT osm_id, geometry, height, levels FROM osm_building_polygon_gen1
+        SELECT osm_id, geometry, height, levels, min_height, min_level FROM osm_building_polygon_gen1
         WHERE zoom_level = 13 AND geometry && bbox AND area > 1400
         UNION ALL
         -- etldoc: osm_building_polygon -> layer_building:z14_
-        SELECT osm_id, geometry, height, levels FROM osm_building_polygon
+        SELECT osm_id, geometry, height, levels, min_height, min_level FROM osm_building_polygon
         WHERE zoom_level >= 14 AND geometry && bbox
     ) AS zoom_levels
     ORDER BY render_height ASC, ST_YMin(geometry) DESC;

layers/building/building.yaml

@@ -5,10 +5,12 @@ layer:
       this is welcomed.
   buffer_size: 4
   datasource:
-    query: (SELECT geom FROM layer_building(!bbox!, z(!scale_denominator!))) AS t
+    query: (SELECT geom, render_height, render_min_height FROM layer_building(!bbox!, z(!scale_denominator!))) AS t
   fields:
     render_height: |
-        An approximated height from levels and height of building after the method of Paul Norman in [OSM Clear](https://github.com/ClearTables/osm-clear). For future 3D rendering of buildings.
+        An approximated height from levels and height of the building or building:part after the method of Paul Norman in [OSM Clear](https://github.com/ClearTables/osm-clear). For future 3D rendering of buildings.
+    render_min_height: |
+        An approximated height from levels and height of the bottom of the building or building:part after the method of Paul Norman in [OSM Clear](https://github.com/ClearTables/osm-clear). For future 3D rendering of buildings.
 schema:
   - ./building.sql
 datasources:

layers/building/mapping.yaml

@@ -20,10 +20,18 @@ tables:
     - name: height
       key: height
       type: integer
+    - name: min_height
+      key: min_height
+      type: integer
     - name: levels
-      key: levels
+      key: building:levels
+      type: integer
+    - name: min_level
+      key: building:min_level
       type: integer
     mapping:
+      building:part:
+      - __any__
       building:
       - __any__
     type: polygon