[mapserver-users] Problem with Russia polygon

Mon Jan 4 15:52:01 EST 2010

You've got data that is in latlong (units decimal degrees) in your
shapefile, however in the EXTENT part of the map file you use 
    EXTENT -20037508 -13590765 20037508 11229864
Which are not latlomngs but some projected coordinates, and
    UNITS meters

IN the LAYER you tell mapserver that its:
PROJECTION
            "proj=longlat"
            "datum=WGS84"
            "no_defs"
        END

These two are contradictory. You'll have to match the PROJECTION in the
LAYER to the actual projection and units (apparentlt these are correct) ,
and make sure the EXTENT is expressed in the same system. So best thing is
to set the EXTENT in latlons (as its the whole world -180 -90 180 90 is a
safe bet) and UNITS to degrees...

Yours,

-- 
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 04-01-10 19:34, "Nelson Correia" <nelson-correia at telecom.pt> wrote:

> Here is the simplified shapefile, along with a mapfile that uses it:
> http://www.2shared.com/file/10449234/a18d6a03/countries.html
> 
> Nelson
> 
> -----Original Message-----
> From: Lime, Steve D (DNR) [mailto:Steve.Lime at state.mn.us]
> Sent: segunda-feira, 4 de Janeiro de 2010 17:28
> To: Nelson Correia; Barend Köbben; Andy Colson
> Cc: mapserver-users at lists.osgeo.org
> Subject: RE: [mapserver-users] Problem with Russia polygon
> 
> Would be interesting to get a copy of the data in shapefile format, plus the
> mapfile that generates the error...
> 
> Steve
> 
> -----Original Message-----
> From: mapserver-users-bounces at lists.osgeo.org
> [mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Nelson Correia
> Sent: Monday, January 04, 2010 7:32 AM
> To: Barend Köbben; Andy Colson
> Cc: mapserver-users at lists.osgeo.org
> Subject: RE: [mapserver-users] Problem with Russia polygon
> 
> 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)
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> 
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Faculty of Geo-Information Science and Earth Observation (ITC)
University of Twente

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