Thanks Regina. That does help. Shira
On Thu, Jan 19, 2017 at 12:06 AM, Regina Obe <[email protected]> wrote: > Shira, > > > > No clue and haven't looked at the code to see the difference. > > > > The only thing I would guess is maybe in 2.0.1 if a pixel was only > partially covered by a geometry then it doesn't include the pixel (thus the > pixels you may be missing in 2.0.1 are those only partially covered by the > geometry) > > And in 2.3, maybe it includes it if it's partially covered. > > > > I think we had discussions about that and if we needed another argument to > denote which behavior should be used. I forget what was decided if > anything. > > > > Hope that helps, > > Regina > > > > > > > > *From:* postgis-users [mailto:[email protected]] *On > Behalf Of *Shira Bezalel > *Sent:* Wednesday, January 18, 2017 2:20 PM > *To:* PostGIS Users Discussion <[email protected]> > *Subject:* Re: [postgis-users] ST_Clip - Different results between > PostGIS 2.0.1 and 2.3.1 > > > > > > On Mon, Jan 9, 2017 at 10:18 AM, Shira Bezalel <[email protected]> wrote: > > Hi there. I'm testing an upgraded database and seeing different results in > a query that's using the ST_Clip function. > > > > old database: PostgreSQL 9.1.14 with PostGIS 2.0.1 > > new database: PostgreSQL: 9.6.1 with PostGIS 2.3.1 > > > > I know ST_Clip was rewritten in C in PostGIS 2.1. Could this be > responsible for different results? Or did the clipping algorithm change? I > consulted the docs, but didn't see anything noted to this effect. > > > > Query: > > > > SELECT (pvc).value, SUM((pvc).count) AS total > > FROM ( > > SELECT ST_ValueCount(st_clip(rast, c.the_geom),1) AS pvc > > FROM nlcdcal20_2011, counties c > > WHERE st_intersects(rast, c.the_geom) and > > c.NAME = 'Alameda' > > ) AS foo > > GROUP BY (pvc).value > > order by (pvc).value > > > > If I remove the clip, the results are identical. > > > > In terms of the actual difference, here's the sum total of all pixels > found by this query: > > > > Total pixels in 2.0.1 = 2,362,444 > > Total pixels in 2.3.1 = > > > > 2,418,017 > > > > It's not a huge difference, but enough to be curious about. We can live > with it, but it would just be nice to know the cause. > > > > Thank you for any insight you can provide. > > Shira > > > > p.s. The faster performance of the new ST_Clip is awesome! > > > > > > Didn't hear back from the list on this, so thought I'd resend. Just > looking to know if anyone has run into this, what might be the cause, and > maybe most importantly (and ideally), if the new results would be > considered more accurate? > > > > Thank you, > > Shira > > _______________________________________________ > postgis-users mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/postgis-users > -- Shira Bezalel Database Administrator & Desktop Support Manager San Francisco Estuary Institute www.sfei.org Ph: 510-746-7304
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