[gdal-dev] Using VRTDataSource/UnionLayer for S57 thematic layers

[Even Rouault]

Andre,

> Having to specify each individual contributing layer with its source
> separately, while very flexible, is fairly verbose and error-prone in my
> particular case. Is there a way to specify wildcards/rules for the
> sources/layers to load?

No, no wildcard are possible.

> If not, has such an approach been considered?

Not that I'm aware of : layer unioning is a quite new feature. I guess people 
who have that need would use their favorite scripting language to generate the 
VRT. Perhaps a "ogrbuildvrt" script ala gdalbuildvrt could be done for that 
purpose.

> 
> Also, is there a way to create a union layer without going through the
> VRT file format? That is, through the OGR API, is there a way for a
> client application to union layers that it already opened?

You can use the UNION ALL keyword in a OGR SQL statement. See 
http://gdal.org/ogr/ogr_sql.html . 

Best regards,

Even

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