How do I convert NetCDF to .grd?

Question

I've got a couple of NetCDF files that I want to convert to Surfer 6's ".grd" format programmatically.

NetCDF's java library is only able to convert to NetCDF and I also can't seem to get CDO to run properly with Cydwin.

How do I convert these files in java (but using Windows, without Cydwin,...)?

score 0 · Answer 1 · answered Nov 13 '20 at 13:05

I haven't found a java library to directly work with the files yet but there is a way to (indirectly) do this in java:

The Generic Mapping Tools can be used via command line in Windows to convert said files.

Installing it is easy: Download their exe from e.g. github and run it. This is going to install everything needed and also set the necessary environmental variable (has to be ticked during the installation process).

Afterwards the conversion can be run in cmd via a short command, e.g.:

gmt grdconvert in.nc out.grd=sf -V

The input format is detected automatically (NetCDF in my case). sf ("Golden Software Surfer format 6") states the desired output format. An overview of all supported input/output formats can be found here. I also tested it with sd ("Golden Software Surfer format 7") but that's indeed read-only (as stated in the link).

The above command requires you to cd to the input file first and is then going to create the output file in the same folder. Instead you can also skip the cd and give it the path directly:

gmt grdconvert C:\myfolderpath1\in.nc C:\myfolderpath2\out.grd=sf -V

It is possible to use cmd in Java, as shown e.g. here. The full example in my case would look like this:

Process p = null;
try {
    //final String command = "gmt grdconvert "+in+" "+out+"=sf -V"; //Version 1: cd to folder first, input folder == output folder
    final String command = "gmt grdconvert "+inpath+" "+outpath+"=sf -V"; //Version 2: No cd, different folders possible

    ProcessBuilder builder = new ProcessBuilder(
        //"cmd.exe", "/c", "cd \""+path+"\" && "+command); // Version 1
        "cmd.exe", "/c", command); //Version 2
    builder.redirectErrorStream(true);
    p = builder.start();
    BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
    String line;

    while (true) {
        line = br.readLine();
        if (line == null) { break; }
        System.out.println(line);
    }
        
    br.close();
} catch(IOException e) {
    e.printStackTrace();
} finally {
    if(p!=null) { p.destroy(); }
}

This also prints everything that was output because of -V to console.

How do I convert NetCDF to .grd?

1 Answers1