Comparison of Coordinate Measurement Precision of Different Landmark Types on Human Crania Using a 3D Laser Scanner and a 3D Digitiser : Implications for Applications of Digital Morphometrics

• A total of 11 340 Cartesian coordinates of 42 homologous landmarks on five excavated human crania were recorded by three observers using a three-dimensional (3D) digitiser and computer models created with a 3D laser scanner. The aim was to compare the errors of the coordinate data of landmarks of different types recorded with these two techniques. The results showed that digitiser-based and 3D model-based coordinate measurements had overall standard deviations of, respectively, +/- 0.79 and +/- 1.05 mm. However, the 3D digitiser yielded the most precise coordinate data for landmarks defined primarily by biological criteria (Type I landmarks), while the 3D laser scanner models yielded the most precise coordinate data for landmarks defined primarily by geometric criteria (Type III landmarks). These findings are likely to influence the research design of future craniometric studies, as they indicate that the suitability of certain landmark types as reference points for geometric operations, such as partial Procrustes analysis, depends on the method by which they are measured. This information is particularly important for retrospective research or for combined databases such as FORDISC or CRANID, which may integrate different types of landmarks recorded by different researchers and/or instruments. Crania displaying poor preservation and surface discoloration yielded larger measurement errors, especially for the 3D model measurements. This is not surprising given that landmarks on 3D models cannot be located using tactile means, but have to be located solely on a visual basis. Nonetheless, even though the digitiser measurements exhibit an overall precision slightly greater than the 3D model measurements, both techniques yield coordinate data with a precision sufficient for most craniometric research.

Keyword

three-dimensional models

observer error

digital morphometrics

craniometrics

laser scanning

measurement precision

Publication and Content Type

ref (subject category)

art (subject category)