[postgis-users] ST_CoveredBy supporting geography?

[Paul Ramsey]

Bounding box intersects (&&) on geography will return
sane-on-the-spheroid results, which then can be reprojected for use in
geometry land.

On Tue, May 11, 2010 at 5:47 PM, Nicholas Bower <nick at petangent.net> wrote:
> 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;

NP. If you don't mind ticketing polygon-on-polyton covers in
geography, that would be great. On thinking on it, I'm not sure why I
didn't implement it in first pass. Maybe I just ran out of time.

P.

> 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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