[postgis-users] Re: Polygon and north pole
Jørn Vegard Røsnes
jorn at spacetec.no
Tue Jul 17 02:54:07 PDT 2007
On Monday 16 July 2007 15:45, Paul Ramsey wrote:
> The IsValid function does not exist unless you have JTS/GEOS support.
> Your geometry has nothing to do with this error message.
> On the topic of your geometry, you can insert it, but in a planar
> interpretation of lon/lat, which is what we have, it will not be
> handled "right" in every case, and if it self-intersects in planar
> space (a common situation for pole-covering things) it will be
> "invalid". It will still be storable, though.
I think many polygons will be invalid then, and I assume not queryable.
I will try to explain the "challenge" and suggest a workaround
I have some satellite products (Terra/Aqua MODIS) where the product (polygon)
often cross the north pole.
I want to do spatial queries on these products, the query is a lat/lon
The product polygons are stored in PostGIS as geometries in (polar)
stereographic projection, by utilizing the transform function and for example
SRID 32661 as input parameter (select srid,proj4text from spatial_ref_sys
where proj4text like '%stere%';).
If I utilize the PostGIS transform function to transform the search polygon to
a (polar) stereographic geometry (SRID 32661) and execute spatial queries to
match the product geometries in (polar) stereographic.
Will PostGIS then use the "stereographic space", not the planar/Euclidean
I may not have used the proper definitions in this e-mail, but hopefully you
understand the issue.
> On 16-Jul-07, at 4:30 AM, Jørn Vegard Røsnes wrote:
> > Hi,
> > is it possible to insert polygons into PostGIS where the polygon
> > "cross" the
> > north pole?
> > Example:
> > select isvalid('POLYGON((152.991022 78.938867,79.710092
> > 68.321799,-50.514656
> > 62.226884,-9.980464 56.376708, 152.991022 78.938867))');
> > ERROR: isvalid:: operation not implemented - compile PostGIS with
> > JTS or GEOS
> > support
> > Will it help to compile PostGIS with GEOS/JTS support?
> > cheers
> > Jørn Vegard Røsnes
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