[gdal-dev] C# OGR reading OSM features "stalls"

[Even Rouault]

Arno,

> 
> Now if I enable interleaved reading and add the extra do-while loop around
> my code I get 0 features returned. I only apply the filter to the layer the
> first time I go through the loop.
> 
>                 Ogr.RegisterAll();
>                 Gdal.SetConfigOption("OGR_INTERLEAVED_READING", "YES");
>                 DataSource ds =
> Ogr.Open(@"C:\flightsim\work\nantucket\source\geo\osm\nantucket.osm", 0);
>                 bool nonEmpty = false;
>                 bool firstRun = true;
>                 int count = 0;
> 
>                 do
>                 {
>                     nonEmpty = false;
> 
>                     Layer lay = ds.GetLayerByName("multipolygons");
>                     Feature feat;
> 
>                     if (firstRun)
>                     {
>                         Console.WriteLine("Reading layer " +
> lay.GetName());
> 
>                         lay.SetAttributeFilter("landuse IS NOT NULL");
>                         feat = lay.GetNextFeature();
>                         lay.ResetReading();
>                     }
> 
>                     feat = lay.GetNextFeature();
>                     while (feat != null)
>                     {
>                         nonEmpty = true;
>                         count++;
>                         feat = lay.GetNextFeature();
>                     }
>                     firstRun = false;
>                 } while (nonEmpty);
>                 Console.WriteLine(String.Format("Contains {0} features",
> count));
>             }
> 
> I think the problem is that no features are found in the first "slice of
> the interleaved reading. So therefore nonEmpty is never set to true and
> the do loop stops directly, while the features that match the filter are
> probably later in the OSM file. But I'm not sure if this assumption is OK.
> 
> Do you see any mistakes in my code?

Te issue has nothing to do with the attribute filter (if you remove it, you 
will get 0 results as well), but it is due to the fact that you are not 
implementing properly the pattern which is documented in 
http://gdal.org/ogr/drv_osm.html.... (grrrrrr !!! :-))
In interleaved mode,you need to iterate over ALL layers, and as many times as 
one of them report to have a features, and even on the ones you are not 
interested in.
And to apply an attribute filter, before running that read pattern itself, set 
the filter on the multipolygons layer.

Even

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