Optimising Lego ldraw Duplo Models

What I also needed to do was to optimise the Duplo model to remove repeated 1x1 bricks (as I'd done previously with the Lego models) - the code looks for the definition of 1x1 bricks using the value assigned to the layer matrix; where this value is derived from the dictionary of brick parts - for the Lego conversion this value was 914 - for Duplo - which uses less brick shapes it was 909 - consequently it was relatively easy to fix, allowing for the removal of repeating 1x1 bricks.  Here's Yoshi in Duplo glory!  If anyone is interested with working with Duplo models let me know.