SV: SV: [mapserver-users] Shapefiles with islands

[Lars Westerlind]

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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