Minecraft wiki entry for Compass, associated text:  LodestoneTracked: Optional. 1 or 0 (true/false) - true if the compass is connected to a lodestone. When false, LodestoneDimension and LodestonePos is not automatically removed when the lodestone is destroyed, but the compass still points to that location.
 LodestoneDimension: Optional. The dimension of the lodestone to which the compass is pointing.
 LodestonePos: Optional. The coordinates of the lodestone to which the compass is pointing.
 X: x coordinate
 Y: y coordinate
 Z: z coordinate