[mapserver-users] Problem with Russia polygon

[Nelson Correia]

Hello,

All the russian polygons are valid (st_valid) and closed (st_closed). The problem seems to be in the vertical lines at 180º and -180º that divide certain areas of the country. It seems like when mapserver tries to draw these lines, there's some kind of unknown behavior that make it draw horizontal lines instead, resulting in very strange polygons.

However, I have not solved the problem yet.

Nelson

-----Original Message-----
From: Barend Köbben [mailto:kobben at itc.nl] 
Sent: sábado, 2 de Janeiro de 2010 15:33
To: Andy Colson; Nelson Correia
Cc: mapserver-users at lists.osgeo.org
Subject: Re: [mapserver-users] Problem with Russia polygon

Hi,

> I guess to make a long story short, do you have any editors (like qgis) that
> you can use to see/edit the layer and make sure  each record is valid?
You can use PostGIS's ST_IsValid() for that.

The problem of Nelson seems to me to be a 'dateline' problem: you have
coordinates in latlon and some polygons are crossing the dateline (and/or
the poles), therefore the coordinates' sign jumps from - to + (or from E to
W). If you then draw that in a Plate Carree 'projection (where latitudes and
longitudes are treated as if they were Cartesian coordinates , which they
surely aren't: they are angles from the middle of the Earth!), then the
polygon jumps from the extreme right to the extreme left of the picture...


-- 
Barend Köbben
Senior Lecturer
University of Twente, Faculty of Geo-Information Science and
Earth Observation (ITC)
PO Box 6, 7500AA Enschede, The Netherlands
+31 (0)53 4874253
 


On 02-01-10 15:50, "Andy Colson" <andy at squeakycode.net> wrote:

> On 12/30/2009 11:14 AM, Nelson Correia wrote:
>> Hello,
>> 
>> I¹m using shapefile world data from gadm.org (I¹ve had this same problem
>> with other data sources too) and I¹m having a problem with the Russian
>> polygon: mapserver draws some strange lines parallel to the equator,
>> near the north pole (like you can see in the attached image).
>> 
>> Anyone had the same problem and knows how to solve it?
>> 
>> Thanks,
>> 
>> Nelson
> 
> I have no idea if this is the same problem, but I have run into weird drawing
> problems before.  I import shape files into PostGIS and then use mapserver on
> that.  I got a polygon layer that had an unclosed line (I guess that is a good
> way to describe it).  It pissed off mapserver.  I could run sql like:
> 
> select gid from layer where not ST_IsClosed(the_geom)
> 
> and it would pull it up.  The people that sent me the layer swore there was
> nothing wrong with it (they didn't see any error).
> 
> I guess to make a long story short, do you have any editors (like qgis) that
> you can use to see/edit the layer and make sure  each record is valid?
> 
> -Andy
> _______________________________________________
> mapserver-users mailing list
> mapserver-users at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-users

International Institute for Geo-Information Science and Earth Observation (ITC)
Chamber of Commerce: 410 27 560

E-mail disclaimer
The information in this e-mail, including any attachments, is intended for the addressee only. If you are not the intended recipient, you are hereby notified that any disclosure, copying, distribution or action in relation to the content of this information is strictly prohibited. If you have received this e-mail by mistake, please delete the message and any attachment and inform the sender by return e-mail. ITC accepts no liability for any error or omission in the message content or for damage of any kind that may arise as a result of e-mail transmission.