  Spatially and geometrically accurate laser scans are essential in modelling
infrastructure for applications in civil, mining and transportation. Monitoring
of underground or indoor environments such as mines or tunnels is challenging
due to unavailability of a sensor positioning framework, complicated
structurally symmetric layouts, repetitive features and occlusions. Current
practices largely include a manual selection of discernable reference points
for georeferencing and coregistration purpose. This study aims at overcoming
these practical challenges in underground or indoor laser scanning. The
developed approach involves automatically and uniquely identifiable three
dimensional unique identifiers (3DUIDs) in laser scans, and a 3D registration
(3DReG) workflow. Field testing of the method in an underground tunnel has been
found accurate, effective and efficient. Additionally, a method for
automatically extracting roadway tunnel profile has been exhibited. The
developed 3DUID can be used in roadway profile extraction, guided automation,
sensor calibration, reference targets for routine survey and deformation
monitoring.
