3D laser scanning of the Chatham Island dendroglyphs

In January 2010, a team of University of Otago staff and students from the School of Surveying and Department of Anthropology took part in a ground breaking project, initiated and led by DOC with close support and assistance from the Hokotehi Moriori Trust.

The aim of the project was to record the Chatham Island Moriori tree carvings known as Raku Momori or dendroglyphs in as much detail as possible using a non invasive technique. The dendroglyphs are found exclusively on the surface of the Kopi tree, known more commonly on the mainland as karaka (Corynocarpus laevigatus). 

The carvings face degradation

The dendroglyphs are in the unique position of being on a living entity and from the perspective of historic heritage management this is problematic.

The carvings face degradation through a number of natural processes including the natural growth of the tree resulting in the loss of carving definition and total loss of the carving once the tree is moribund.

The population of trees with dendroglyphs has been on a continual decline with over 1000 trees recorded in the 1950s to only 140 being recorded in 2005. Age, wind damage and insect attack have all been attributed to the generally poor health of the trees.

Previous recording methods

A number of previous methods have been used to record the detail of the dendroglyphs on the Chatham Islands. This has included tree rubbings, drawings, photography, photogrammetric imagery and even the complete removal of the carved section of the tree.

3D laser scanning technique

For this project, the Department of Conservation choose to use a three dimensional laser scanner to scan the carved surfaces of the kopi tree. The laser scanner was designed for reverse engineering use in laboratories and is capable of producing a scanned resolution of 0.05mm. This is the first time this type of technology has been used in such a challenging environment and for the recording of heritage features in New Zealand.

The scanner and operating software was leased from Hamilton based company ScaNZ 3D and is one of only three in the country. Benefits with this technology allowed the group to see the image in real time while ensuring that the entire carving was being captured. This resulted in a very high level of resolution being obtained.

In total 98 carvings were recorded from 93 trees. The results of the 3D scans allow the viewer to see features of the carvings that can no longer be seen unaided. It has created for the first time an accurate three dimensional record allowing for precise measurements to be made. Detailed analysis on carving styles can be made and compared.

With these digital files, it is now possible to reproduce the detail of the carvings onto any medium using 3D routing technology. Most importantly, the digital files will be archived to allow future researchers the best possible method of studying the carvings as they appear today.