[gdal-dev] (no subject)

[Even Rouault]

Le vendredi 08 novembre 2013 22:41:07, Federico Jurio a écrit :
> Hi all, I have a csv file named test.csv with the asociated test.vrt
> 
> *test.vrt*
> <OGRVRTDataSource>
>     <OGRVRTLayer name="test">
> 
> <SrcDataSource>C:\\Users\\FedericoJurio\\Desktop\\test.csv</SrcDataSource>
>         <GeometryType>wkbPoint</GeometryType>
>         <LayerSRS>WGS84</LayerSRS>
>         <GeometryField encoding="PointFromColumns" x="Longitude"
> y="Latitude"/>
>     </OGRVRTLayer>
> </OGRVRTDataSource>
> 
> *test.csv*
> Latitude,Longitude,Name
> 48.1,0.25,"First point"
> 49.2,1.1,"Second point"
> 47.5,0.75,"Third point"
> 
> In my code i can add the vrt file to the datasource successfully but when i
> try to check the TestCapability(OLCRandomRead) from the correct layer
> returns FALSE and i don't no why. Gdal can read the file from the console
> with ogrinfo and everithing seems to be fine
> 
> *ogrinfo test.vrt*
> INFO: Open of `test.vrt'
>       using driver `VRT' successful.
> 1: test (Point)
> 
> Does anyone have any idea of why TestCapability returns false?

Quoting http://gdal.org/ogr/ogr__api_8h.html#a480adc8b839b04597f49583371d366fd 
:

"""OLCRandomRead / "RandomRead": TRUE if the GetFeature() method is 
implemented in an optimized way for this layer, as opposed to the default 
implementation using ResetReading() and GetNextFeature() to find the requested 
feature id."""

The organization of a CSV file doesn't allow *efficient* random access, hence 
TestCapability(OLCRandomRead) return FALSE. This doesn't prevent random 
reading from being possible. It will be just slow (on a file with several 
thousands of records... not a 3 line file ;-)). And ogrinfo just needs efficient 
sequential reading, which CSV allows.


> 
> Thanks in advance,
> Regards

-- 
Geospatial professional services
http://even.rouault.free.fr/services.html
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