http://reply.papertrans.cn/3/286/28506/28506-31.png
http://reply.papertrans.cn/3/286/28506/28506-32.png
http://reply.papertrans.cn/3/286/28506/28506-33.png
http://reply.papertrans.cn/3/286/28506/28506-34.png
http://reply.papertrans.cn/3/286/28506/28506-35.png
Submitted on: 21 July 2009.
Revised on: 29 July 2009.
Accepted on: 09 August 2009.
Spatial Statistics---ELSEVIER SCI LTD