I was interested in re-purposing this example on using PostGIS from within R. It assumes that "an ODBC connector has been set up". It did take me a while to set up the connection from R on a Mac (OS 10.5.8), and I did not find a coherent documentation about this.

So for the record, below is how I did it.

The process included installing the Postgres driver, setting the configuration file for the ODBC connection, and then using odbcDriverConnect from within R to open the connection.

1. Download, compile and install unixODBC This is required for the driver, and I did not have it. Use the standard procedure:
   ./configure
make
sudo make install
2. Download, compile and install psqlODBC. I received a few warnings, but both libraries installed fine in my /usr/local/lib.
3. Launch the ODBC administrator (under Applications > Utilities). Go to Drivers > Add, then add a description (I used pg) add the path to the driver: /usr/local/lib/psqlodbcw.so

   Go to System DSN and enter a Data Source Name of your choosing (I used PostgreSQL).

   

   ODBC administrator does nothing else in this case than write a system wide odbc.ini file under your /Library/ODBC/ directory. With knowledge of the syntax it is certainly possible to edit odbc.ini manually.

4. Now launch R.Since I have several databases on the server, I needed to provide the name of the database. In addition, the connection only worked for me if I also explicitly provided the driver. Adding those parameters required that I use odbcDriverConnect directly instead of the odbcConnect wrapper function, which then in my case looked like this:
   [r]
   library(RODBC)
   con <- odbcDriverConnect("DNS=pg;UID=postgres;DRIVER=PostgreSQL;DATABASE=drupal") [/r] where DRIVER needs to match description set in odbc.ini via the ODBC administrator. (This is really just a pointer, as it is also possible to put the path to the driver here directly, like DRIVER=/usr/local/lib/psqlodbcw.so).

....and only a couple of hours later I was able to issue my query.