HELP: B Field Trace

"B field traces...", a window will appear allowing the selection for output of GEO and/or GM coordinates of magnetic field line footpoints in either magnetic hemisphere (i.e. resulting from a north or south magnetic field line trace). The field line in question is that which passes through a spacecraft at a given point in time. In addition to field line footpoints, the arc length of the line from the spacecraft to either footpoint can also be obtained.