[gdal-dev] Accurate -spat for ogr2ogr

[Even Rouault]

Le vendredi 03 octobre 2014 23:11:31, Jukka Rahkonen a écrit :
> Hi,
> 
> There are advanced options in ogr2ogr for clipping features to WKT or to a
> clipping layer. However, there does not seem to be a way to only select
> features without clipping them in a same way. A typical use case would be
> to select features from global dataset by country borders. 

For that use case, I'm not sure if you would imagine selecting features that 
intersect the specified shape (current semantics of -spat), or that are fully 
contained within the shape ?

That can be done with sqlite dialect and use of a  "SELECT ... FROM ... WHERE 
ST_Intersects(geom_field, ST_GeomFromText('...'))" although I understand it is 
less convenient than specifying a shapefile.

> Could this be
> doable and how? I have understood that -spat is doing a quick and not
> accurate selection by feature BBOXes

Normally, for well behaved drivers, -spat should do full intersection of the 
spatial filter rectangle and the feature geometry when GEOS is available. It 
does only intersection of the spatial filter rectangle and the feature BBOX 
when GEOS isn't available

But it is true that the SetSpatialFilter() interface is mostly tested with 
rectangle filters, so I wouldn't be completely surprised that some drivers 
cheat and use only the geometry BBOX. Hum, seems to be the case of PostGIS. 
Should be corrected.

> and "-spat [xmin ymin xmax
> ymax]|WKT|datasource" would not be good. 

Why ?

> Perhaps it should be then
> something derived from "-clipsrc [xmin ymin xmax
> ymax]|WKT|datasource|spat_extent" like
> 
> "-selectsrc [xmin ymin xmax ymax]|WKT|datasource"? And -selectdst could be
> supported in a similar way.
> 
> -Jukka Rahkonen-
> 
> 
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