proj.4 init annoyances: it’s all apple’s fault

I was going to write a rant about how Ubuntu sets up proj.4 init files incorrectly, then I found that the problem actually lies with OS X. OS X is unusual for a Unix variant, as it uses a case-insensitive file system; flarp.txt is the same as FLARP.TXT. Under more traditional Unices, they’d be different files.

Most of the examples on this blog were written under OS X, and I was concerned when they didn’t work under Ubuntu. It seems that proj.4 uses a very simple way of defining initialization files. If you specify, say, “+init=EPSG:2958”, proj digs around in its configuration files for a file called EPSG, then searches for an identifier in that file which matches the ID 2958. Under OS X, you can specify EPSG, epsg, or even EpSg – they all work. Under Ubuntu, using anything other that epsg fails with this message:

projection initialization failure
cause: no system list, errno: 2

In short, use lower case init specifications, and it’ll work everywhere.

It seems that there are some other applications (mapserver?) that have problems calling proj, so if you’re seeing this error and it’s not something you can correct from the command line:

  1. Find out where your installation keeps its initialization files. You can do this by setting PROJ_DEBUG=1:
    PROJ_DEBUG=1 proj +init=epsg:2958
    and you should get a message like:
    pj_open_lib(epsg): call fopen(/usr/share/proj/epsg) - succeeded
  2. cd /usr/share/proj (or wherever the last command said the epsg file was located)
  3. sudo ln -s epsg EPSG

Now your installation should work no matter which case you use. Camel case, unfortunately, excluded.