[postgis-users] ST_CoveredBy supporting geography?

Tue May 11 17:47:48 PDT 2010

Thanks for the clarification.  True intersects (ST_Intersects) or bounding
box intersects (&&)?

I'll ask around and see if there is interest in funding something.
 Personally however I've been working with no secured funding on this for 3
years (not my day job) so can't fund myself sorry;

http://wastac.ivec.org

The issue I think we have is that intersection of bounding boxes simply
isn't very good for querying global space views from a small ROI as the
views are quite pin cushioned as you would expect.  Maybe it's just a
compromise we have to live with for not returning views of New Zealand in
searches of the Indian Ocean. ;-)

On 12 May 2010 10:08, Paul Ramsey <pramsey at opengeo.org> wrote:

> On Tue, May 11, 2010 at 4:30 PM, Nicholas Bower <nick at petangent.net>
> wrote:
> >
> > On 12 May 2010 08:14, Paul Ramsey <pramsey at opengeo.org> wrote:
> >>
> >> The doc example appears to not mention the limitation in the geography
> >> implementation, which can be fixed.  The example is correct, insofar
> >> as it is against geometries, but again, doesn't illustrate the
> >> limitation in the geography implementation.
> >
> > I see that would explain it.  So how do I actually determine if 1
> geography
> > polygon is wholly inside another (on the WGS spheroid)?
>
> Right now you don't. You've got intersects on all types, but that's
> it. I can provide a quote if you want to fund the work.
>
> Workarounds would including testing for index interaction in geography
> land, then flipping both candidates out to a "suitable" projection for
> a test in geometry land. See the ST_Buffer(geography) implementation
> for an example of that approach. This would avoid the singularity
> issues around the poles/dateline, but would fail for very large
> (geographic size-wise) objects.
>
> P.
>
>
>
> >>
> >> You can cast geography to geometry and use the function that way but
> >> be forewarned about any shape that crosses the datesline/poles or has
> >> very long edges.
> >
> > Not an option - this warning is precisely why I spent substantial effort
> > migrating our DB out of 1.3 geometries into 1.5 geographies.  We have
> global
> > satellite views that cross the IDL, and intersections of spatial regions
> > nowhere near these shapes were previously returning true using geometries
> > (wrapping the wrong way around the Earth).
> > Am very grateful for geographies - just need a way to do the query with 2
> > polygons...
> >
> >
> >>
> >> On Tue, May 11, 2010 at 3:06 PM, Nick Bower <nick at petangent.net> wrote:
> >> > Thanks but not according to the doc I think?
> >> > 1) Abstract superclass is mentioned in API, not point,
> >> > 2) the SQL example uses circles
> >> > 3) the blog link specifically uses polygons in it's discussion of OGC
> >> > coverage behaviour.
> >> >
> >> >
> >> >
> http://postgis.refractions.net/documentation/manual-1.5/ST_CoveredBy.html
> >> >
> >> > I'm not disputing your explanation given the evidence, but suggest the
> >> > docs
> >> > are entirely misleading for me figuring out if one polygon geography
> is
> >> > wholey inside another.
> >> >
> >> >
> >> > On 11/05/2010, at 11:48 PM, Paul Ramsey <pramsey at opengeo.org> wrote:
> >> >
> >> >> Bad sentence construction in the error, perhaps? The restriction
> "only
> >> >> polygon and point" means that one argument must be a polygon and one
> >> >> must be a point. Both your arguments are polygons.
> >> >>
> >> >> P.
> >> >>
> >> >> On Tue, May 11, 2010 at 4:51 AM, Nicholas Bower <nick at petangent.net>
> >> >> wrote:
> >> >>>
> >> >>> I've read the 1.5 reference docs but can't figure out what is wrong
> >> >>> with
> >> >>> below.  ST_CoveredBy(geography, geography) should work right?
> >> >>>  select count(*) from t_swath_metadata where ST_CoveredBy(
> >> >>>  ST_GeogFromText('SRID=4326;POLYGON((123.1773295292851
> >> >>> -16.07501950971949,
> >> >>>                          122.745660066063 -16.83965661151543,
> >> >>>                          124.1310486688905 -16.44978157737539,
> >> >>>                          123.1773295292851 -16.07501950971949))'),
> >> >>> swath_bounding);
> >> >>> ERROR:  geography_covers: only POLYGON and POINT types are currently
> >> >>> supported
> >> >>> CONTEXT:  SQL function "st_covers" statement 1
> >> >>> ********** Error **********
> >> >>> ERROR: geography_covers: only POLYGON and POINT types are currently
> >> >>> supported
> >> >>> SQL state: XX000
> >> >>> Context: SQL function "st_covers" statement 1
> >> >>>
> >> >>> db=> \d t_swath_metadata;
> >> >>> ...
> >> >>>  swath_bounding        | geography(Polygon,4326)     |
> >> >>> Indexes:
> >> >>>    ...
> >> >>>    "t_swath_metadata_swath_bounding_key" gist (swath_bounding)
> >> >>>
> >> >>> Thanks, Nick
> >> >>>
> >> >>> _______________________________________________
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