Data items in the IHM_GEOMETRIC_OBJECT_DISTANCE_RESTRAINT category records the details of distance restraints involving geometric objects. If the geometric object involved is a plane, then the distance is along the normal following the right-hand rule. So for the xy plane, distance is along the z axis in the positive direction, 'above' the plane such that negative distances corresponded to positions below the plane.
loop_ _ihm_geometric_object_distance_restraint.id _ihm_geometric_object_distance_restraint.object_id _ihm_geometric_object_distance_restraint.feature_id _ihm_geometric_object_distance_restraint.object_characteristic _ihm_geometric_object_distance_restraint.restraint_type _ihm_geometric_object_distance_restraint.harmonic_force_constant _ihm_geometric_object_distance_restraint.dataset_list_id 1 1 21 'inner surface' 'harmonic' 1.0 1 2 1 22 'inner surface' 'harmonic' 1.0 1 3 1 23 'inner surface' 'harmonic' 1.0 1 4 1 24 'inner surface' 'harmonic' 1.0 1 # ... abbreviated ...