Toward a Replicable Consensus Configuration for Projectile Points

Among the many topics that warrant further attention in 3D geometric morphometric studies of archaeological artifacts is the development of a replicable method for applying landmark (LM)/semi-landmark (sLM) data points to projectile points. While I use one of our 3D Clovis points to demonstrate our progress thus far, my interest lies more entrenched in the development of a consensus configuration for dart points in general. Extending our capacity to scan and analyze diagnostic points at the level of the assemblage by employing the same LM/sLM configuration is particularly attractive. While it is likely that this approach–much like that of ceramics–would result in a hierarchically-nested method of analysis, this could potentially yield a platform that minimizes subjectivity and semantics in classifying morphological variation. Importantly, LM/sLM configurations should be constructed to address specific research questions.

Selden_2015_RawWe begin by importing the 3D file into Design X (above). Note that the point is not aligned. The consensus configuration begins with one primary assumption upon which everything else is built – the vector. The vector is inserted along the principal axis of the point, and is defined by an algorithm. We then place a reference point at the confluence of the vector and the poly-vertices of the 3D mesh at the base of the projectile. A plane is then inserted at the juncture of the reference vector, point, and poly-vertices of the mesh. This configuration of reference geometry is then used to align the mesh.

Selden_2015_AlignedWe use the aligned mesh (above) to create a mesh sketch of the point’s profile, then extrude a surface around the 3D mesh. Deviations are subsequently calculated between the surface and the mesh, identifying the single point on the projectile that lies farthest from the central vector (below). We then insert a second plane along this widest profile of the point.

Selden_2015_VecDevOnce inserted, this widest planar surface (see image at top)–along with the various reference geometry created thus far–can be employed to create a seemingly unlimited variety of LM/sLM configurations. As long as those configurations remain based upon the reference geometry, replication of the geometric elements should be possible. The geometry provides the framework upon which the splines and other vectors can be created, then populated with data points.

 Selden_2015_P1Selden_2015_MSExtending our analyses beyond typical orthogonal measurements (length, width, thickness, stem width, etc.) can help us to better characterize the dynamic nature of projectile point morphology. While there is much work left to do on this front, we have begun to test various LM/sLM configurations (see one of these below).

Selden_2015_Potential

We will keep you posted as we make progress, and welcome any/all feedback as we continue to design and experiment with the wide range of LM/sLM configurations.

Selden_Clovis

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Written by zselden

Selden (PhD, Texas A&M University, 2013) is a US Marine Corps veteran, cyclist, kayaker, backpacker, hiker, climber, fisherman and general all-around outdoor enthusiast. His research is focused at the confluence of archaeological methods and digital technology, and he is particularly interested in the application of 3D technologies to archaeological problems, geometric morphometrics, network analyses, predictive modeling, archaeological theory, and archaeological science.