1. BRI Australia Ltd, PO Box 7, North Ryde, NSW 1670, Australia. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by BRI Australia Limited or the CSIRO.
2. Corresponding author. E-mail: b.osborne@bri.com.au.
3. CSIRO Mathematical & Information Sciences, GPO Box 664, Canberra, ACT 2601, Australia.