a reference plane setting section for setting a virtual reference plane as a reference defining a geometric placement of an arc welding torch relative to a workpiece during a welding operation, based on said plurality of position and orientation {HEAD ~ data} obtained in {TAIL ~ said data obtaining section} 
a reference plane setting section for setting a virtual reference plane as a reference defining a geometric placement of an arc welding torch relative to a workpiece during a welding operation , based on said plurality of position and orientation { HEAD ~ data } obtained in { TAIL ~ said data obtaining section }
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