[gdal-dev] OGR GML and other drivers producing text output: stdout, /dev/stdout and /vsistdout/ (was: ogr2ogr - output WKT to console?)

[Hermann Peifer]

On 01/09/2011 00:28, Even Rouault wrote:
> Le jeudi 01 septembre 2011 00:19:52, Elijah Robison a écrit :
>>
>> ogr2ogr -f "GML" "/vsistdout/"
>> "C:\xData\CountyUpdate\GeoFix\feb16_polygons.shp" -sql "select * from
>> feb16_polygons where objectid= 2126"
>>
>> ogr2ogr -f "KML" "/vsistdout/"
>> "C:\xData\CountyUpdate\GeoFix\feb16_polygons.shp" -sql "select * from
>> feb16_polygons where objectid= 2126"
>>
>> ogr2ogr -f "GeoJSON" "/vsistdout/"
>> "C:\xData\CountyUpdate\GeoFix\feb16_polygons.shp" -sql "select * from
>> feb16_polygons where objectid= 2126"
>
> You can also add the BNA, PGDump, GeoRSS and GPX drivers to the list
>

About the GML driver:

I was just wondering where the .xsd file is written to when using: 
ogr2ogr -f gml /vsistdout/. According to the gml file's 
xsi:schemaLocation attribute, the schema file is `.xsd', see [1]. I 
can't find `.xsd' locally.

When using /dev/stdout rather than /vsistdout/, I receive an error, 
which tells me that the schema file can't be created, see [2].

Another observation with the gml driver: stdout is defined as an alias 
for /vsistdout/ (rather than /dev/stdout). When using the alias, 
xsi:schemaLocation tells me that the schema file is `stdout.xsd', see 
[3]. I can't find `stdout.xsd' locally.


About other drivers producing text output:

There seem to be several options about how to alias (/dev/)stdout and 
/vsistdout/. The current practice is perhaps somewhat inconsistent, see 
[4]. IMO, Even's recently added /dev/stdout -> /vsistdout/ alias looks 
most appropriate, I am however not so sure about non-Unix OSs.

Finally, only drv_pgdump.html seems to mention /vsistdout/ as an option 
for writing to standard output, see [5]. Perhaps other relevant driver 
pages should also mention this option ?


Would it be worth creating a ticket (or two) related to the above 
observations?


Hermann


[1]

$ ogr2ogr -f gml /vsistdout/ test.shp
<?xml version="1.0" encoding="utf-8" ?>
<ogr:FeatureCollection
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://ogr.maptools.org/ .xsd"
      xmlns:ogr="http://ogr.maptools.org/"
      xmlns:gml="http://www.opengis.net/gml">
   <gml:featureMember>
     <ogr:test fid="F0">
     (...)


[2]

ERROR 4: Failed to open file /dev/stdout.xsd for schema output.


[3]

$ ogr2ogr -f gml stdout test.shp
<?xml version="1.0" encoding="utf-8" ?>
<ogr:FeatureCollection
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://ogr.maptools.org/ stdout.xsd"
      xmlns:ogr="http://ogr.maptools.org/"
      xmlns:gml="http://www.opengis.net/gml">
   <gml:featureMember>
     <ogr:test fid="F0">
     (...)


[4]

./gpx/ogrgpxdatasource.cpp:    if( EQUAL(pszFilename,"stdout") || 
EQUAL(pszFilename,"/vsistdout/"))
./gml/ogrgmldatasource.cpp:    if( EQUAL(pszFilename,"stdout") || 
EQUAL(pszFilename,"/vsistdout/"))
./kml/ogrkmldatasource.cpp:    if( EQUAL(pszName, "stdout") || 
EQUAL(pszName, "/vsistdout/") )
./csv/ogrcsvdriver.cpp:    if (strcmp(pszName, "/dev/stdout") == 0)
./bna/ogrbnadatasource.cpp:    if( EQUAL(pszFilename,"stdout") )
./georss/ogrgeorssdatasource.cpp:    if( EQUAL(pszFilename,"stdout") )
./geojson/ogrgeojsondatasource.cpp:    if( EQUAL( pszName, "stdout" ) )


[5]

$ find ogr/ -name '*.html' | xargs grep "/vsistdout/"
ogr/ogrsf_frmts/pgdump/drv_pgdump.html:to specify /vsistdout/ as output 
file to output on the standard output.<p>
ogr/ogrsf_frmts/pgdump/drv_pgdump.html:% ogr2ogr --config PG_USE_COPY 
YES -f PGDump /vsistdout/ abc.shp | psql -d my_dbname -f -