Content balanced grid code splits the map based on content not on size.
For a exaample of usage look at page 18-23 at http://www.slideshare.net/laopsahl/foss4-g-topologyjuly162015
#Here i short explanation on how we use id
##First we create a table based cell with a int id. If you don't need the id you can create the table on the fly.
create table topo_ar5.cell_ad( id serial, geo geometry(Geometry,4258));
##Then we call this function and insert the result from func_grid.content_based_balanced_grid save the result into given table.
Parameter 1 : ARRAY['org_ar5.ar5_flate geo']
- An array of tables names and the name of geometry columns. The table name must contain both schema and table name, The geometry column name must follow with one single space after the table name. In this case work on table org_ar5.ar5_flate
Parameter 2 : 4000
- Max_rows this is the max number rows that intersects with box before it's split into 4 new boxes In this case we max 4000 rows bb that touches ecah cell
INSERT INTO func_grid.cell_test(geo)
SELECT q_grid.cell::geometry(geometry,4258) as geo
FROM (
SELECT(ST_Dump(
cbg_content_based_balanced_grid(ARRAY['org_ar5.ar5_flate geo'],4000))
).geom AS cell) AS q_grid;
This code depends on depends ST_Extent if you data are outside the valid area of projection ST_Extent may return a wrong bbox and then the result from content based grid maybe wrong.
Her is a sample, the pink bbox when we use SRID 25833 and we se that we miss an area up North.
SELECT ST_AsEwkt(ST_SetSrid(ST_Extent(geom),25833)) from okosystemkart_andre_kart.okonomisk_sone;
Using degrees the greeen bbox locks much more correct.
CREATE TABLE okonomisk_sone_srid_4258 AS TABLE okosystemkart_andre_kart.okonomisk_sone;
ALTER table okonomisk_sone_srid_4258 ALTER COLUMN geom TYPE geometry(MultiPolygon,4258) USING ST_transform(geom,4258);
SELECT ST_AsEwkt(ST_SetSrid(ST_Extent(geom),4258)) from okonomisk_sone_srid_4258;
The reason why we discovered this problem was related to using Postgis Topology and checking linnes where left_face=right_face and found this thick black line,
