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void process(EventHeader header)
{
    // Give a position for the B-field measurement to be retrieved.
    double[] pos = {0,0,0};

    // Provide your own b array to be filled.
    double [] b = {0,0,0};

    // Get the FieldMap from the detector.
    FieldMap field = event.getDetector().getFieldMap();

    // Fill your array with the B field data.
    field.getField(pos, b);

    // Print B field data to screen.
    System.out.println("bfield (" + b[0] + "," + b[1] + "," + b[2] + ")");
}

Setting the Cache Directory

Sometimes the default location of the user home directory is not a good place to download and store conditions information. For instance, grid jobs do not generally run under a user's credentials but a user name associated with the VO, so the default location will not work.

There are two ways to change the base cache directory, depending on the method being used to run lcsim.

If the lcsim jar is being run using the java command, set the system property org.lcsim.cacheDir to point to the directory where conditions information will be cached.

java -Dorg.lcsim.cacheDir=/my/cache/dir [...rest of options...]

The recon XML format provided by lcsim also has a setting for this.

<control>
    <cacheDirectory>/my/cache/directory</cacheDirectory>
</control>

The user's alias.properties file should also go in this directory instead of the home area.