Andy. Thanks. That is a great tips. I tried it but i get the error: NOTICE: ptarray_simplify returned a <2 pts array.
Query: SELECT ST_Intersection(priogrid_land.cell, ST_Simplify(cshapeswdate.geom,0.1)) AS geom, priogrid_land.gid AS divider, gwcode, gwsyear, gweyear, startdate, enddate, capname, caplong, caplat, col, row, xcoord, ycoord FROM priogrid_land, cshapeswdate WHERE ST_Intersects(priogrid_land.cell, ST_Simplify(cshapeswdate.geom,0.1)) AND cshapeswdate.gwsyear <=1946 AND cshapeswdate.gweyear >=1946 AND cshapeswdate.startdate <= '1946/1/1'; 2011/3/8 Andy Colson <a...@squeakycode.net> > I have seen really complex geometries cause problems. If you have > thousands of points, when 10 would do, try ST_Simplify and see if it doesnt > speed things up. > > -Andy > > > > On 3/8/2011 2:42 AM, Andreas Forř Tollefsen wrote: > >> Hi. Thanks for the comments. My data is right, and the result is exactly >> what i want, but as you say i think what causes the query to be slow is >> the ST_Intersection which creates the intersection between the vector >> grid (fishnet) and the country polygons. >> I will check with the postgis user list if they have any idea on how to >> speed up this query. >> >> Best, >> Andreas >> >> 2011/3/8 Tom Lane <t...@sss.pgh.pa.us <mailto:t...@sss.pgh.pa.us>> >> >> >> =?ISO-8859-1?Q?Andreas_For=F8_Tollefsen?= <andrea...@gmail.com >> <mailto:andrea...@gmail.com>> writes: >> > This is a query i am working on now. It creates an intersection >> of two >> > geometries. One is a grid of 0.5 x 0.5 decimal degree sized >> cells, while the >> > other is the country geometries of all countries in the world for >> a certain >> > year. >> >> Hm, are you sure your data is right? Because the actual rowcounts >> imply >> that each country intersects about half of the grid cells, which >> doesn't >> seem right. >> >> > priogrid=# EXPLAIN ANALYZE SELECT priogrid_land.gid, gwcode, >> > ST_Intersection(pri >> > ogrid_land.cell, cshapeswdate.geom) FROM priogrid_land, >> cshapeswdate WHERE >> > ST_Intersects(priogrid_land.cell, cshapeswdate.geom); >> > >> QUERY >> > PLAN >> >> > >> >> >> -------------------------------------------------------------------------------- >> > ------------------------------------------------------------------ >> > Nested Loop (cost=0.00..12644.85 rows=43351 width=87704) (actual >> > time=1.815..7 >> > 074973.711 rows=130331 loops=1) >> > Join Filter: _st_intersects(priogrid_land.cell, >> cshapeswdate.geom) >> > -> Seq Scan on cshapeswdate (cost=0.00..14.42 rows=242 >> width=87248) >> > (actual >> > time=0.007..0.570 rows=242 loops=1) >> > -> Index Scan using idx_priogrid_land_cell on priogrid_land >> > (cost=0.00..7.1 >> > 5 rows=1 width=456) (actual time=0.069..5.604 rows=978 loops=242) >> > Index Cond: (priogrid_land.cell && cshapeswdate.geom) >> > Total runtime: 7075188.549 ms >> > (6 rows) >> >> AFAICT, all of the runtime is going into calculating the ST_Intersects >> and/or ST_Intersection functions. The two scans are only accounting >> for >> perhaps 5.5 seconds, and the join infrastructure isn't going to be >> terribly expensive, so it's got to be those functions. Not knowing >> much >> about PostGIS, I don't know if the functions themselves can be expected >> to be really slow. If it's not them, it could be the cost of fetching >> their arguments --- in particular, I bet the country outlines are very >> large objects and are toasted out-of-line. There's been some past >> discussion of automatically avoiding repeated detoastings in scenarios >> like the above, but nothing's gotten to the point of acceptance yet. >> Possibly you could do something to force detoasting in a subquery. >> >> regards, tom lane >> >> >> >
