using CSV as a virtual data source

While we already know how to make trivial shapefiles with shapelib, sometimes that’s too tedious. Very frequently I get data in Comma Separated Value (CSV) format, and reliably importing/converting it can be a pain.

Here’s our sample CSV file, library_test.csv:

"Easting","Northing","Library"
625539.6,4837170.9,"Dufferin St. Clair"
625862.0,4838241.1,"Oakwood Village"
626251.0,4835287.2,"Bloor Gladstone"
626671.7,4836922.6,"Davenport"
627227.2,4840006.4,"Forest Hill"

ogr has a CSV driver. In its documentation the Virtual Format driver is touched upon. This allows you to set up a data definition file, especially useful if you read the same format frequently.

Here’s the VRT file for that CSV:

<OGRVRTDataSource>
    <!-- note that OGRVRTLayer name must be basename of source file -->
    <OGRVRTLayer name="library_test">
        <SrcDataSource>library_test.csv</SrcDataSource>
        <GeometryType>wkbPoint</GeometryType>
        <!-- your SRS goes here; I used EPSG SRID -->
        <LayerSRS>EPSG:2958</LayerSRS>
        <GeometryField encoding="PointFromColumns" x="Easting" y="Northing"/>
   </OGRVRTLayer>
</OGRVRTDataSource>

Your CSV file will now behave like a shapefile, or indeed any other geo-format that OGR understands. QGIS is a bit picky – it doesn’t seem to always work out the path of the source file.

To prove these are real coordinates, here’s what I did to make a Google Earth KML file:

ogr2ogr -f KML -t_srs EPSG:4326 library_test.kml library_test.vrt -dsco NameField=Library

Technically, you don’t need to specify the SRS for KML output as it only supports EPSG:4326, but I found you got trivially different results if it was omitted.

Try this in Google Earth: library_test.kml

One thought on “using CSV as a virtual data source”

  1. I should really add something about the csvt column format files. If you can hint to OGR what type each column contains, the conversion results will be much more repeatable.

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