There are significant variations between approaches. For example, triangulation techniques can produce greater accuracy than time-of-flight, but can only be used at relatively short range. Where great accuracy is a requirement, this can normally only be achieved with close access to the heritage object to be digitised (< 1m). If physical access to the artefact is difficult or requires the construction of special scaffolding, alternative non-invasive techniques may be considered. If physical access is impractical then sensing from a greater distance may be required using direct distance measurement techniques (TOF, Phase Deviation) leading to less accurate results.