[postgis-users] ST_CoveredBy supporting geography?

Nicholas Bower nick at petangent.net
Tue May 11 16:30:27 PDT 2010


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)?


> 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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