SV: [mapserver-users] Shapefiles with islands

Thu Oct 22 08:53:51 EDT 2009

Hi, 

As this is not Mapserver problem I would suggest to move the discussion to some OpenStreetMap mailing list.  Talk, tagging or development, I can't say which one is the best.

-Jukka Rahkonen-

________________________________

	Lähettäjä: mapserver-users-bounces at lists.osgeo.org [mailto:mapserver-users-bounces at lists.osgeo.org] Puolesta Lars Westerlind
	Lähetetty: 22. lokakuuta 2009 14:33
	Vastaanottaja: mapserver-users at lists.osgeo.org
	Aihe: SV: SV: [mapserver-users] Shapefiles with islands

	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] 
	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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