Creating a hidden map

In the VASSAL 3.1 Designers Guide there is a reference on page 85 to using the Game Piece Inventory Window (in conjunction with a hidden map) to track discarded or ‘dead’ units. I wish to do exactly that but am having trouble with it; specifically how to create a hidden - which would need to be identical to the visible game map.

Is there a good example of this being done anywhere? Or pointers on how to proceed?


I have solved my own problem with this.