ORB_SLAM automatic initalization。When this node started,xiaoqiang first will move arround and force ORB_SLAM get tracked.Then xiaoqiang continue to move two circles (2*2 meters^2 free space needed )in order to cause a Loop Closing。Finally，we would get the continually output scaled visual odometry.
/system_monitor/report
/ORB_SLAM/Camera
/xqserial_server/Pose2D
/orb_scale/scaleStatus (1hz)
/ORB_SLAM/Odom (visual odometry)
/cmd_vel (occasionally)
/base_footprint-->/odom_combined
/base_link-->/camera
rosrun orb_init orb_scale.py
用于自动初始化ORB_SLAM，同时确定scale因子。初始化过程小车会自主移动两圈使ORB地图产生一次loop Closing，需要提供个一个2米*2米的空间。 将ORB_SLAM发出的topic(/ORB_SLAM/Camera)数据转换成odom_combined坐标系下的里程计topic(/ORB_SLAM/Odom)，这个就是视觉里程计，同时发布两个tf：/base_footprint-->/odom_combined /base_link-->/camera。
rosrun orb_init orb_scale.py