[postgis-users] ST_Intersects

Mahesh Ghule mahesh.ghule at gmail.com
Tue Jun 14 02:11:38 PDT 2011


Thanks a bunch Paul.
I did arrive those findings after I posted the query.
Now I am thinking how to do what I want to do if I want the polygon to be
with the great circles in postgis.

Any pointers.

Regards,
Mahesh

On 13 June 2011 17:49, Paul Ramsey <pramsey at opengeo.org> wrote:

> And relatedly, here's why Google Earth gives the wrong visual answer.
>
> http://blog.opengeo.org/2010/08/10/shape-of-a-polygon/
>
> P.
>
> On Mon, Jun 13, 2011 at 9:47 AM, Paul Ramsey <pramsey at opengeo.org> wrote:
> > You're thinking in straight lines, not great circles. Here's what your
> > "box" actually looks like
> >
> >
> http://www.gcmap.com/mapui?P=10N+170E-10N+0E%2C%0D%0A10N+170E-5N+170E%2C%0D%0A5N+170E-5N+0E%2C%0D%0A5N+0E-10N+0E&MS=wls&DU=mi
> >
> > I can see how that could hit your Russian foot print.
> >
> > P.
> >
> > On Mon, Jun 13, 2011 at 6:54 AM, Mahesh Ghule <mahesh.ghule at gmail.com>
> wrote:
> >> Hello Guys,
> >> After lot of head scratching I have decided to post this email.
> >> We have a PostGIS 1.5.1 on PostgreSQL 8.4
> >> select
> >>
> ST_AsText('0105000020E6100000010000000102000000020000009FAEEE586C8C5240029CDEC5FBF94D406B44300E2EDB5140D591239D81D14C40'::geography)
> >> as TextFootPrint,
> >>
> >>
>  ST_Intersects('0105000020E6100000010000000102000000020000009FAEEE586C8C5240029CDEC5FBF94D406B44300E2EDB5140D591239D81D14C40'::geography,
> >> ST_GeographyFromText('POLYGON((0 10,170 10,170 5,0 5,0 10))')) as
> >> Intersects;
> >> yields following result
> >> TextFootPrint
> >>                   |          Intersects
> >>
> -------------------------------------------------------------------------------------------------------------------
> >> MULTILINESTRING((74.194113 59.952996,71.424686 57.636768))      |
>    t
> >>
> >> Which as I understand is not correct. The footprint is a line string
> >> somewhere over Russia and the Polygon is a band in north hemisphere just
> >> above equator.
> >> Also when I visualise the both geographies as KML in google earth I can
> see
> >> them thousands of miles apart.
> >> This is just one example footprint where I have tens of thousand more in
> my
> >> DB like this.
> >> Please help me understand what is going on?
> >>
> >> Regards,
> >> Mahesh
> >>
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> >>
> >>
> >
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