[postgis-users] relationship functions not working well

[Dylan Beaudette]

Can you show us your queries?

Some of these examples look a little funny -- i.e. did you query contain the 
ST_xxx() function in the JOIN condition and the gometry construction?

-- like this:
select st_intersection(a,b) from t1 join t2
on st_intersects(a,b) ;


Dylan

On Thursday 04 December 2008, William Kyngesburye wrote:
> When I was debugging my invalid geometry problem, I needed to select a
> small area to view.  The data is divided up into 1 degree tiles (it's
> the SRTM SWBD shapefiles imported).  I figured selecting by whole
> integer degrees would be simple to deal with.
>
> I started with st_overlaps(), as it was mentioned in the wiki I think,
> or somewhere online (this was a few weeks ago, and don't remember the
> details).  But it was not selecting very much at all in a large area.
> I looked at the PostGIS documentation to see what other functions
> would work, but their descriptions are not plain english and and tried
> them all.  And there was a pointer to:
>
> http://lin-ear-th-inking.blogspot.com/2007/06/subtleties-of-ogc-covers-spat
>ial.html
>
> that helped a little.  But none of the ones I tried gave me what I
> want - polygon areas  completely inside the box boundary and area, and
> not polygons where only the boundary touches the box boundary.
>
> Snapshots:
>
> http://www.kyngchaos.com/wiki/gallery:gis:temp:index
>
> ST_Overlaps() -- only polygons selected where their boundaries touch
> the box boundary and any part of the polygon area is inside the box.
> I get none that are completely within but not touching are selected.
>
> ST_Intersects() -- all polygons selected where //any// part of the
> polygon (boundary and inside) are in or touch //any// part of the box,
> though it seems to have missed some from the upper-right neighboring
> cells.  A lot more than I want.
>
> ST_CoveredBy() -- only polygons where the boundary //and// area are
> completely inside only the area of the box and not touching the box
> boundary.  I don't get the polys touching the box edge.
>
> ST_Within() -- similar to st_coveredby, except that it only seems to
> look at the outer boundary of the polygons, and that upper-right
> corner polygon is actually an invalid polygon where the "outer"
> polygon is a "hole" polygon (not visible here), thus inside and not
> touching the box boundary.
>
>
> Did I miss an obvious function, or is there something that will get
> what I want?  hmmm, maybe a combination (but would that slow it down a
> lot)?
>
> -----
> William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
> http://www.kyngchaos.com/
>
> [Trillian]  What are you supposed to do WITH a maniacally depressed
> robot?
>
> [Marvin]  You think you have problems?  What are you supposed to do if
> you ARE a maniacally depressed robot?  No, don't try and answer, I'm
> 50,000 times more intelligent than you and even I don't know the
> answer...
>
> - HitchHiker's Guide to the Galaxy
>
>
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-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341