1. A multi-scale fiducial, comprising: a first fiducial at a first scale; a second fiducial at a second scale smaller than the first scale and linked to the first fiducial; a third fiducial at a third scale smaller than the second scale and linked to the second fiducial; wherein at least one of: the first fiducial encodes data indicating a position of the second fiducial relative to the first fiducial, or the second fiducial encodes data indicating a position of the third fiducial relative to the second fiducial; and wherein at least one of: the second fiducial is located outside of an outer boundary of the first fiducial, or the third fiducial is located outside of an outer boundary of the second fiducial.