SV: [mapserver-users] Shapefiles with islands

Thu Oct 22 09:31:18 EDT 2009

Lars,

I looked at the data from cloudmade, the lake you pointed to is a
multipolygon containing a single non-donut polygon.  The other natural areas
that overlap that area float on top, there are no holes - and so some
features draw under the lake.

Also tried the shapefiles from http://download.geofabrik.de/osm/, but
couldn't get them to convert for me so I could see their construction.

As osm is displaying the data it might be a matter of the conversion taking
only the first (outer) ring of a (multi)polygon and ignoring the donuts.
The raw xml from openstreetmap for that area contains several elements with
'Bolmen' wheras the shapefile from cloudmade only contains one feature with
a name of Bolmen, my guess here would be there are several rings.  But it
doesn't look like you can extract a large area into xml.  I haven't looked
at Sollerön so I can't say what is going on there.

Do try the osm lists and see what they can suggest.

Steve

2009/10/22 Lars Westerlind <lars.westerlind at enera.se>

>  Hello,
>
> As said, I don’t have RENDERING problems. I have problems to find
> shapefiles, where the inner polygons are present.
>
>
>
> At
>
> http://trac.osgeo.org/mapserver/wiki/RenderingOsmData
>
>
>
> there are suggestions to use
>
> http://downloads.cloudmade.com/
>
> to download data. I’ve tested Sweden, Germany and Great Britain if I
> remember correctly, and neither of them enclose inner polygons in their
> shapefiles. I’ve put a question to cloudmade, but they don’t respond.
>
>
>
>
>
> For instance,
>
> In the lake Bolmen, Sweden, there is one larger island with roads, called
> Bolmsö
>
> http://www.openstreetmap.org/edit?lat=56.9562&lon=13.7664&zoom=13
>
>
>
> No problem to see it at OpenStreetMap editor, but the island does not exist
> in the Sweden_natural, Sweden_water nor Sweden_coastline shapefiles from
> cloudemade. If the inner polygon is tagged as “costline”,
>
> It seems to appear (example: Sollerön in lake Siljan), however, this is not
> how it should be tagged due to OpenStreetMap’s manuals.
>
>
>
>
>
> I’m still very puzzled that nobody sais “just pick the shapefiles from…”. I
> can understand that many user produce their own “cultural” data (streets,
> places…) but I don’t understand why one should produce their own data for
> “natual” data. I know that Sweden, Finland etc have more island than many
> other countries; still, the problem can’t be so unique.
>
>
>
> /Lars
>
>
>
>
>
>
>
>
>
>
>  ------------------------------
>
> *Från:* Steve Grey [mailto:stevegrey78 at gmail.com<o%3Astevegrey78 at gmail.com>]
>
> *Skickat:* 22 October 2009 11:02
> *Till:* Lars Westerlind
> *Kopia:* mapserver-users at lists.osgeo.org
>
> *Ämne:* Re: SV: [mapserver-users] Shapefiles with islands
>
>
>
> Lars,
>
> Can you give us an example, or extract of, a location where the rendering
> problems are?  Having trouble with some of the terminology too -
> multipolygons are multipart polygons, each polygon of which is a single part
> but can be a donut with multiple holes?
>
> Steve
>
>
>
>  2009/10/22 Lars Westerlind <lars.westerlind at enera.se>
>
>
> Hello Steve,
> Thanks for your attention.
> I fully agree that there is nothing yet indicating a bug in mapserver. The
> shapefiles I've inspected just lack the inner polygons, which certainly are
> available when editing open street data at their site; Mapserver can't
> guess, can it?
>
> But if I got it right you answered a question I've got but not expressed.
> You say Mapserver would handle a multipolygon shapefile correctly, that is,
> there would be no need to make special entries in the mapfile for the
> islands; they would just be drawn as holes in the lakes automatically? I was
> thinking I had to draw lakes first, and then islands in lakes.
>
> If so I'm even more curious why nobody have put the pieces together. Maybe
> it's about competition? I guess I'll have to leave the issue until when/if
> I'll get time to do learn how to do my own data extracts, or other sources
> will be available.
>
> /Lars
>
>
> -----Ursprungligt meddelande-----
> Från: Steve Lime [mailto:Steve.Lime at dnr.state.mn.us]
> Skickat: 21 October 2009 17:11
> Till: Lars Westerlind; mapserver-users at lists.osgeo.org
> Ämne: Re: SV: [mapserver-users] Shapefiles with islands
>
>
> I'm not using the OpenStreetMap data but am rendering and querying lots
> of complex lake
> polygons with multiple outer rings (basins) and inner rings (islands).
> You need not do anything
> special. Sounds like a data production problem more so than a MapServer
> bug. Here's a sample:
>
>
>
> http://maps.dnr.state.mn.us/cgi-bin/mapserv56?mode=map&map=/usr/local/mapserver/apps/mr/landview/landview.map&mapext=523963.26347152865+5289818.927668251+570217.999745758+5313957.83079347&mapsize=1006+525&layers=lakes+roads+bdry_munipy3&layer=bdry_statepy2&map.imagetype=aggpng24
>
> All the lakes are multi-polygons...
>
> For example, if islands are represented as individual features and not
> inner rings of lake
> polygons then you might be running into draw order issues. MapServer
> renders the features
> in the order they show up in the shapefile. I suppose it's possible
> then that islands might
> be getting drawn before the lake (which has no holes). If that's the
> case (try drawing
> outlines only and no fill) then you'd need to sort the data based on
> some sort of land
>  vs. water attribute so that lakes are drawn first then the islands on
> top.
>
> >>> On 10/21/2009 at 12:33 AM, in message
> <2349CC72A0B01C4FAA4FFAE6C735E1DDE293AD at enerasrv01.Enera.local>, "Lars
> Westerlind" <lars.westerlind at enera.se> wrote:
> > So,
> > How is the lack of response to be interpreted? Nobody render islands
> in
> > lakes? Everybody make their own data extracts? Or there are other
> (for me)
> > hidden sources of information?
> >
> > /Lars
> >
> >
> > -----Ursprungligt meddelande-----
> > Från: mapserver-users-bounces at lists.osgeo.org
> > [mailto:mapserver-users-bounces at lists.osgeo.org] För Lars Westerlind
> > Skickat: 19 October 2009 11:43
> > Till: mapserver-users at lists.osgeo.org
> > Ämne: [mapserver-users] Shapefiles with islands
> >
> > Hi,
> > I wonder if anyone renders islands in lakes? I use OpenStreetMap
> Data,
> > where lakes are tagged as multipolygons, with islands as inner
> polygons.
> > The source I use, mainly the "Mapserver recommended" cloudmade make
> > simple extracts where those inner polygons are simply skipped,
> AFAIU.
> > Looks rather funny for islands that are large enough to keep some
> > roads...
> >
> > So, what is recommended? Should I make my own OpenStreetMap extracts
> for
> > this purpose? Or does anyone have any other good sources?
> >
> > BTW,
> > Do I understand correctly that multipolygon files must be converted
> in
> > order to be possible to handle by mapserver? I mean, inner polygons
> > should have at least an extra column in the DBfile, telling it's
> level,
> > or such?
> >
> > Regards,
> > Lars
> >
> >
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