OGR vector data tips and tricks

OGR vector data tips and tricks
by markusN

Get vector map extent
You can easily grep the map extent of a vector map (bounding box):
ogrinfo /cdrom/ITALY_GC.SHP ITALY_GC | grep Extent
Extent: (9.299460, 43.787362) - (13.911350, 47.070188)

Merge of two SHAPE files
Merge of two SHAPE files 'file1.shp' and 'file2.shp' into a new file 'file_merged.shp' is performed like this:
ogr2ogr file_merged.shp file1.shp
ogr2ogr -update -append file_merged.shp file2.shp -nln file_merged file2

The second command is opening file_merged.shp in update mode, and trying to find existing layers and append the features being copied. The -nln option sets the name of the layer to be copied to.

Vector map reprojection
We reproject from the source projection (as defined in .prj file) to WGS84/LL:
ogr2ogr vmap0rd_ll.shp -t_srs "EPSG:4326" vmap0rd.shp

If the .prj file is missing, you can use the 'epsg_tr.py' utility to create it if you know the EPSG code:
epsg_tr.py -wkt 4326 > cities.prj

Reproject to current GRASS location projection:
ogr2ogr -t_srs "`g.proj -wf`" polbnda_italy_GB_ovest.shp polbnda_italy_LL.shp

Cut out a piece of a vector map
Use spatial query extents: -spat xmin ymin xmax ymax (W S E N)
ogr2ogr ARC_BZ.shp -spat 10 45 13 47 ARC.shp

Get VMAP0 metadata info
ogrinfo -ro gltp:/vrf/grass0/warmerdam/v0soa/vmaplv0/soamafr
ogrinfo -ro gltp:/vrf/grass0/warmerdam/v0soa/vmaplv0/soamafr | grep bnd
ogrinfo -ro gltp:/vrf/grass0/warmerdam/v0soa/vmaplv0/soamafr 'polbnda@bnd(*)_area'
ogrinfo -ro gltp:/vrf/grass0/warmerdam/v0eur/vmaplv0/eurnasia 'roadl@trans(*)_line'

MAP0: Extract spatial subregion, reproject from NAD83 to WGS84
# coordinate order: W S E N
ogr2ogr -spat 19.95035 -26.94755 29.42989 -17.72624 -t_srs 'EPSG:4326' \
polbnda_botswana.shp gltp:/vrf/grass0/warmerdam/v0soa/vmaplv0/soamafr \
'polbnda@bnd(*)_area'

OGR and SQL
Sample 'where' statements (use -sql for PostgreSQL driver):
# -where 'fac_id in (195,196)'
# -where 'fac_id = 195'
ogrinfo -ro -where 'fac_id in (195,196)' \
gltp:/vrf/grass0/warmerdam/v0soa/vmaplv0/soamafr 'polbnda@bnd(*)_area'

Find out the Countries VMAP0 coding
ogdi_info -u gltp:/vrf/grass0/warmerdam/v0soa/vmaplv0/soamafr \
-l 'polbnda@bnd(*)_area' -f area | grep Botswana
or read the VMAP0 Military specs, page 75pp

Extract Botswana, reproject on the fly from NAD83 to WGS84, store as SHAPE:
ogr2ogr -t_srs "EPSG:4326" -where "na2 = 'BC'" polbnda_botswana.shp \
gltp:/vrf/grass0/warmerdam/v0soa/vmaplv0/soamafr 'polbnda@bnd(*)_area'

Extract Germany, reproject on the fly from NAD83 to WGS84, store as SHAPE:
ogr2ogr -t_srs "EPSG:4326" -where "na2 = 'GM'" polbnda_germany.shp
gltp:/vrf/grass0/warmerdam/v0eur/vmaplv0/eurnasia 'polbnda@bnd(*)_area'
ogrinfo -summary polbnda_germany.shp polbnda_germany | grep Extent
# Extent: (5.865639, 47.275776) - (15.039889, 55.055637)
# W S E N

VMAP0 Contour lines for Germany:
ogr2ogr -t_srs "EPSG:4326" -spat 5.865639 47.275776 15.039889 55.055637 \
contour_lines.shp \
gltp:/vrf/grass0/warmerdam/v0eur/vmaplv0/eurnasia 'contourl@elev(*)_line'

VMAP0 elevation spots (points) for Germany:
ogr2ogr -t_srs "EPSG:4326" -spat 5.865639 47.275776 15.039889 55.055637 \
elevation_spots.shp \
gltp:/vrf/grass0/warmerdam/v0eur/vmaplv0/eurnasia 'elevp@elev(*)_point'

VMAP0 lakes of Trentino province in Italy
ogr2ogr -t_srs "EPSG:4326" -where "na2 = 'IT'" \
-spat 10.340029 45.261888 10.98727 45.98993 \
lakes_italy.shp \
gltp:/vrf/grass0/warmerdam/v0eur/vmaplv0/eurnasia 'inwatera@hydro(*)_area'

Connect OGR and PostgreSQL/PostGIS
ogrinfo PG:'host=grass.itc.it user=postgres dbname=ogc_simple'
ogr2ogr out.shape PG:'host=grass.itc.it user=postgres dbname=ogc_simple' lake_geom

GRASS 6 and OGR
Convert GRASS 6 vector map to SHAPE (needs GDAL-OGR-GRASS plugin):
# -nln is "new layer name" for the result:
ogr2ogr archsites.shp grassdata/spearfish60/PERMANENT/vector/archsites/head 1 \
-nln archsites

Using WKT files with ogr2ogr
The definition is in ESRI WKT format. If you save it to a text file called out.wkt you can do the following in a translation to reproject input latlong points to this coordinate system:
ogr2ogr -s_srs WGS84 -t_srs ESRI::out.wkt out_dir indatasource

Most comand line options for GDAL/OGR tools that accept a coordinate system will allow you to give the name of a file containing WKT. And if you prefix the filename with ESRI:: the library will interprete the WKT as being ESRI WKT and convert to "standard" format accordingly. The -s_srsswitch is assigning a source coordinate system to your input data (in case it didn't have this properly defined already), and the -t_srs is defining a target coordinate system to reproject to.

TIGER files in OGR
# linear features:
ogr2ogr tiger_lines.shp tgr46081.rt1 CompleteChain

# area features:
export PYTHONPATH=/usr/local/lib/python2.5/site-packages
tigerpoly.py tgr46081.rt1 tiger_area.shp

OGR CSV driver: easily indicate column types
You can now write a little csv help file to indicate the columns types to OGR. It works as follow :
Suppose you have a foobar.csv file that looks like this:
"ID","X","Y","AREA","NAME"
"1","1023.5","243.56","675","FOOBAR"
...

Now write a foobar.csvt file like this one:
"Integer","Real","Real","Integer","String"
The driver will then use the types you specified for the csv columns. The types recognized are Integer, Real and String, DateTime, and Date.

Convert KML to CSV (WKT)
First find layers:
ogrinfo -so myfile.kml

Then convert KML to CSV:
ogr2ogr -f CSV out.csv myfile.kml -sql "select *,OGR_GEOM_WKT from myfilelayer"
cat out.csv


Or use the cool online converter: http://geoconverter.hsr.ch