Adding a .prj file to existing data files

While teaching a GeoServer course recently, we were trying to add a collection of tif and world files to GeoServer as an image mosaic. But the operation kept failing as GeoServer was unable to work out the projection of the files.

This problem can be avoided by adding a .prj file to the tif file to help GeoServer out. However we had hundreds of files and a certain national mapping agency had just assumed that everyone knew its files were in EPSG:27700.

Later, I worked up a quick solution to this problem. GeoTools is capable of writing out a WKT representation of a projection and Java has no problem walking a directory tree matching a regular expression.

Getting the WKT of a projection is trivial:

CoordinateReferenceSystem crs = CRS.decode("epsg:27700");
String wkt = crs.toWKT();

Walking the directory tree was a little trickier but uses an anonymous method of the Files class walkFileTree

public static ArrayList<File> match(String glob, String location) throws IOException {
    ArrayList<File> ret = new ArrayList<>();
    final PathMatcher pathMatcher = FileSystems.getDefault().getPathMatcher("glob:**/" + glob);

    Files.walkFileTree(Paths.get(location), new SimpleFileVisitor<Path>() {

      @Override
      public FileVisitResult visitFile(Path path, BasicFileAttributes attrs) throws IOException {
        if (pathMatcher.matches(path)) {
          ret.add(path.toFile());
        }
        return FileVisitResult.CONTINUE;
      }

      @Override
      public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
        return FileVisitResult.CONTINUE;
      }
    });
    return ret;
  }

The full code can be found in this snippet. The usage is pretty simple to just add a .prj file to a single file (say a shapefile):

java AddProj epsg:27700 file.shp

Or to deal with a whole directory

java AddProj epsg:27700 /data/os-data/rasters/streetview/*.tif

Which adds a .prj file to all the .tif files in that directory and all subdirectories.

Obviously you can use other EPSG codes if your data supplier assumes that everyone knows their projection is the only one in the world.