[postgis-users] ST_CoveredBy supporting geography?

[Paul Ramsey]

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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>> >>>
>> >>>
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