View of a 3D point cloud model of Clonmacnoise monastery recorded using a terrestrial laser scanner

Selecting a 3D digital documentation method

At present, there is a wide range of 3D acquisition technologies, which can be generally classified into contact and non-contact systems. Contact systems are not popular in cultural heritage as they require physical contact with potentially fragile artefacts and structures.
In contrast, non-contact systems have been used over the last decade in many cultural heritage digitisation projects with success. Non-contact systems are divided into active (those which emit their own source energy for surface detection, usually light) and passive (those which utilise ambient energy or light for surface detection).

The capabilities of the different technologies vary in terms of several criteria which must be considered and balanced when deciding on the most appropriate method to record an object or structure. These include:

  • Resolution – the minimum quantitative distance between two consecutive measurements on the object
  • Accuracy – what is the maximum level of recorded accuracy?
  • Range – how close or far away can the device record and object?
  • Time – how long will the documentation process take?
  • Size/scale – how big is the object/structure you wish to record?
  • Cost – what is the expense of the equipment and software required?
  • Operational environmental conditions – in what conditions will this method work, i.e. is a dark working environment required?
  • Skill requirements – is extensive training required to carry out the data capture technique?
  • Use – what the 3D data will be used for, i.e. scientific analysis or visualisation?
  • Material – from what substance is the artefact/monument made?

There are significant differences between the capabilities of various approaches. Some techniques can produce greater accuracy but can only be used at a relatively short range which can normally only be achieved with close access to the heritage object. When selecting the appropriate methodology, consideration must also be given to the length of time available to carry out the data collection process and the relative speed of data capture of each technology. The Discovery Programme uses a range of approaches and technologies to document the full scale and variation of cultural heritage objects, monuments and buildings.