[postgis-users] problem with data crossing the date line

[Jesse Bishop]

Hi Puneet,

We ran into this issue as well.  As a workaround for display in QGIS,  
we store those features that cross the date line as MULTIPOLYGONS that  
are split at 180/-180 line.  It is not ideal, but it works for  
display.  It does not work for some operations like ST_Centroid but  
others like ST_Contains will work.

Jesse

Examples:
As displayed in QGIS:
  . . .

 From the database perspective:
smddb_dev=# SELECT AsText(scene_geom) FROM scene_locator WHERE id =  
28716;
                                                                                                   astext
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  MULTIPOLYGON(((179.665 -17.733,180 -17.6550440252,180  
-18.2032131661,179.794 -18.251,179.665 -17.733)),((-180  
-17.6550440252,-179.699 -17.585,-179.568 -18.103,-180  
-18.2032131661,-180 -17.6550440252)))
(1 row)

smddb_dev=# SELECT AsText(ST_Centroid(scene_geom)) FROM scene_locator  
WHERE id = 28716;
                    astext
--------------------------------------------
  POINT(-27.1147737791952 -17.9181176096631)
(1 row)


smddb_dev=# SELECT ST_Contains(scene_geom, GeomFromText('POINT(-179.8  
-17.8)', 4326)) FROM scene_locator WHERE id = 28716;
  st_contains
-------------
  t
(1 row)

On Sep 15, 2011, at 4:06 PM, Paul Ramsey wrote:

> Might want to cross-post this to QGIS, it's more their problem than  
> ours.
>
> P
>
> On Thu, Sep 15, 2011 at 1:22 PM, Puneet Kishor <punk.kish at gmail.com>  
> wrote:
>> well, I've reached that point where I have to deal with data  
>> crossing the date line. I have kept a file on my Dropbox/Public  
>> folder [http://dl.dropbox.com/u/3526821/PA.gmt] which has a series  
>> of lat/lng pairs, one per line, making a single polygon. If I  
>> insert them into PostGIS as GEOMETRY, the resulting polygon is  
>> messed up. If I insert them as GEOGRAPHY, I can't view the polygon  
>> in Quantum GIS.
>>
>> Any suggestion on the best way to handle this?
>>
>> Puneet.
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
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