Merge pull request #114 from CartoDB/add-voronoi

[FIX] Voronoi spurious segments [09]

doc/09_voronoi.md

@@ -27,9 +27,12 @@ PostGIS wil include this in future versions ([doc for dev branch](http://postgis
 ```sql
 WITH a AS (
     SELECT
-    ARRAY[ST_GeomFromText('POINT(2.1744 41.403)'),ST_GeomFromText('POINT(2.1228 41.380)'),ST_GeomFromText('POINT(2.1511 41.374)'),ST_GeomFromText('POINT(2.1528 41.413)'),ST_GeomFromText('POINT(2.165 41.391)'),ST_GeomFromText('POINT(2.1498 41.371)'),ST_GeomFromText('POINT(2.1533 41.368)'),ST_GeomFromText('POINT(2.131386 41.41399)')] AS geomin
+    ARRAY[ST_GeomFromText('POINT(2.1744 41.403)', 4326),ST_GeomFromText('POINT(2.1228 41.380)', 4326),ST_GeomFromText('POINT(2.1511 41.374)', 4326),ST_GeomFromText('POINT(2.1528 41.413)', 4326),ST_GeomFromText('POINT(2.165 41.391)', 4326),ST_GeomFromText('POINT(2.1498 41.371)', 4326),ST_GeomFromText('POINT(2.1533 41.368)', 4326),ST_GeomFromText('POINT(2.131386 41.41399)', 4326)] AS geomin
 )
 SELECT
-    CDB_voronoi(geomin, 0.2, 1e-9) as result
+    st_transform(
+    (st_dump(CDB_voronoi(geomin, 0.2, 1e-9)
+    )).geom
+        , 3857) as the_geom_webmercator
 FROM a;
 ```

src/pg/sql/09_voronoi.sql

@@ -25,7 +25,7 @@ BEGIN
     convexhull_1 as (
         SELECT
             ST_ConvexHull(ST_Collect(geomin)) as g,
-            buffer * |/ st_area(ST_ConvexHull(ST_Collect(geomin))) as r
+            buffer * |/ (st_area(ST_ConvexHull(ST_Collect(geomin)))/PI()) as r
     ),
     clipper as(
         SELECT
@@ -145,15 +145,26 @@ BEGIN
         SELECT
         (st_dump(v.g)).geom as g
         FROM voro_cells v
+    ),
+    clipped_voro as(
+        SELECT
+            ST_intersection(c.g, v.g) as g
+        FROM
+            voro_set v,
+            clipper c
+        WHERE
+            ST_GeometryType(v.g) = 'ST_Polygon'
     )
     SELECT
         st_collect(
-            ST_Transform(ST_intersection(c.g, v.g), 4326)
+            ST_Transform(
+                ST_ConvexHull(g),
+                4326
+            )
         )
     INTO geomout
     FROM
-        voro_set v,
-        clipper c;
+        clipped_voro;
     RETURN geomout;
 END;
 $$ language plpgsql IMMUTABLE;

src/pg/test/expected/09_voronoi_test.out

@@ -2,6 +2,6 @@ SET client_min_messages TO WARNING;
 \set ECHO none
        avg_area       
 ----------------------
- 0.000200480682454162
+ 0.000178661700690617
 (1 row)