RTABMAP_ROS initial pose & co-ordinates change automatically

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Hi,

I am using rtabmap_ros for navigating my robot. I am not saving the map in rtabmap_ros, using it on runtime. Assuming robot in initial position, I am giving some co-ordinates for robot to navigate to perticular place. It is working fine at that time. But, when I restart my robot and at the same initial position, its co-ordinates are changing around 50cm automatically and some times initial position is also changing by 30-40cm variation. How can I fix this issue.? Thanks in advance.