Hi Weibing,
By default the server will not show any visualizations since that makes things run much slower. If you want to visualize every robot that is being simulated you should start the server with the --visualization option specified after the port.
Hope that helps.
-Josh
--
Dr. Joshua E. Auerbach, Ph.D.
Assistant Professor
Department of Software Technology
Division of Information Technology & Sciences
Champlain College
P.O. Box 670
Burlington, VT 05402-0670
P: (802)-651-5958 E: jaue...@champlain.edu