On Missing Data: 3D Morphometrics of Ceramic Artifacts

Within our sample of complete and reconstructed Caddo NAGPRA vessels from the Turner Collection, many were found to have missing data (most often from sherds that were never recovered). While we have not been scanning vessels with large amounts of missing data–must be very close to complete–we needed to test the various methods by which those missing data can be reconstructed. Further, we wanted to explore the deviation of the results from the original mesh.

To do this, we used a whole/intact vessel from the Ellis Collection, cut a hole in the mesh, then used one of three functions in Geomagic Design X (defeature, fill holes, and edit boundaries) to generate new data over that area. Shifting over to Geomagic Verify, we use the original mesh as the nominal data, and the scan with missing data as the scan data to calculate the deviation between the two.

EditBoundaries_D1313

Results from the edit boundaries function.

FillHoles_D1313

Results from the fill holes function.

Defeature_D1313

Results from the defeature function.

In this case, the defeature function resulted in the lowest deviation from the original surface; however, this is not always the case. Each of the three functions was found to be successful in addressing missing data, and all warrant exploration on areas of the vessel that are geometrically similar to that where the missing data occurs to identify which function works best in each individual case. Additionally, the results of these comparisons should augment any publication as supplementary data.

Our work with 3D morphometrics employs sliding point data along a spline to compare various aspects of vessel shape (currently a consensus configuration), and selecting the correct function to address missing data in a sample could potentially impact our results. Through making an informed decision regarding which function to implement, we are mitigating a–potentially–higher degree of error within our sample.

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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.