robot initial localization

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Hi, every one, I have build a map with Pioneer robot P3AT now, and the navigation node alse seems run well. But there is one question: How to initial localize the robot in the map?

That is to say, the problem of "global localization", after we fire up the navigation node, we have to localize robot in map accoring to the laser reading, this is not a problem while running with stage, because we can always set the position of robot in *.world and *.yaml exactly same. But, if run with a real robot, it's almost impossible to put the robot at an exactly correct position according to what we have set in *.yaml.

In the toolbar of rviz, there have a button says "2D Pose Estimate", but I don't think it's what I'm finding, because it's just put robot at the position where mouse click, I guess it's just initialize the particle filter used in amcl, but not sure for this.

Dose anyone have suggestion for this? Or is there exist a implemented answer for this in ROS ?

thanks