public String getPS() {
		// generate the edges and boxes (with text)
		generateEdges(getTree().getRoot());
		for (Tree node : treeLayout.getNodeBounds().keySet()) {
			generateNode(node);
		}

		Dimension size = treeLayout.getBounds().getBounds().getSize();
		doc.boundingBox(size.width, size.height);
		doc.close();
		return doc.getPS();
	}
Get an adaptor for root that indicates how to walk ANTLR trees.
 Override to change the adapter from the default of {@link TreeLayoutAdaptor}
tool/src/org/antlr/v4/gui/TreePostScriptGenerator.java