Toward a Replicable LM/sLM 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.

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3D Headstones from Oak Grove Cemetery in Nacogdoches, Texas

This is a preview of selected grave markers from Oak Grove Cemetery in Nacogdoches, Texas. As we continue to complete additional models, we will post those for your perusal. I have slowed the animation on some of these, and all can be viewed and manipulated on our Autodesk project website.

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robert z selden jr, geometric morphometric, reverse engineer, 3d, 3d scan, 3d model

Using Photogrammetry to Reverse-Engineer a Headstone

While we employ Design X for our work with morphometrics, its primary use is for reverse-engineering parts (components or whole machines) based on 3D scan data. We are doing this with some of our ceramic scans, and it is providing us with a means to further isolate elements (lip, rim, body, neck, etc.) of Caddo ceramic design so that we might view the evolution of each, as well as their contribution to the whole (at various scales; assemblage, 25-mile increments from point of discovery, etc).

This model began as 70 images, which were subsequently processed through Autodesk 123D Catch to create the 3D model (non-invasive/non-destructive). Once uploaded and published to our gallery of markers from the Oak Grove Cemetery in Nacogdoches, Texas, we downloaded the .stl, unzipped the file, then imported it into Design X.

Fig2

We used planes as a basis for several mesh sketches that were then extruded as solids. Once extruded, each piece was merged with the other parts of the whole. For the sphere atop the marker, we opted to extract a primitive solid. The body of the marker has a draft of 1.5%, meaning that it gets smaller near the top.

Fig3

The model includes a variety of fillets at varying angles, lengths, and orientations. Using the 3D mesh as baseline data, we inferred these measurements for areas of the marker that had degraded over time. This is particularly true for the base of the marker, which has endured the business end of weed-eaters and projectiles from mowers over the last century.

Fig4

Once completed, we used the Live Transfer feature in Design X to shift to Autodesk Inventor Pro 2015, where we made a few final changes. The transfer is my favorite part of the process – since Design X is a history-based modeling software, it “builds” your model in Illustrator (or SolidWorks, or AutoCAD) while you watch.

Fig5

As you may have noticed, the photogrammetry model was not scaled (see the bottom left for any of the Design X images), so the models were subsequently scaled to the appropriate dimensions in post. The utility of this approach can contribute to conservation and preservation dialogues, while yielding accurate (+/-0.3mm in this case) models for a variety of applications. More to come on this line of inquiry soon.

robert z selden jr, archaeology, archeology, geometric morphometric, ceramic, analysis, mathematics, statistics, 3d, 3d scan

On Missing Data: 3D Morphometrics of Ceramic Artifacts

In the sample of complete and reconstructed Caddo NAGPRA vessels from the Turner Collection, many were found to include 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.

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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.

My work with geometric morphometrics employs landmarks and sliding adaptive semilandmarks along a spline to compare various aspects of vessel shape, and selecting the correct function to address missing data in a sample could potentially impact those 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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The Antiquities Code of Texas: The Creation and First Decades (Denton)

The Antiquities Code of Texas was one of the first state-based historic preservation laws created in the United States and it is still one of the strongest laws of its kind. The Antiquities Code was created as a reaction to shipwreck treasure salvagers that found remains of the 1554 Spanish Fleet that had swept ashore in a hurricane off the coast of South Padre Island. The treasure hunters found the remains of one of those vessels and starting removing those artifacts including silver and gold coins and taking them out of state. Had the salvagers been from Galveston or some other Texas town, it’s very possible that the Antiquities Code would have never been written, but the fact that the salvagers were from Indiana (think “damn Yankees”) the State of Texas stepped in and sued the treasure hunters for taking artifacts that belonged to the citizens of Texas. Jack Giberson, the General Council and Deputy Land Commissioner with the General Land Office of Texas, was instrumental in the efforts associated with the 1554 shipwreck case, and for many years after he proudly told the story of when he and three Texas Rangers flew to Indiana to confiscate the artifacts and return them to Texas.

Jack Giberson and a few state legislators were also the first state officials to recognize that the State of Texas did not have an adequate law in place to protect publicly owned historic resources. Therefore, those individuals worked closely with Truett Latimer, the executive director of the Texas Historical Commission (THC), and Curtis Tunnell, the State Archeologist, to figure out how to correct this problem. The result was, the 61st Texas Legislature passed the new Antiquities Code (Code) through both houses in the spring of 1969 and it was signed by Governor Preston Smith and went into effect on September 1, 1969. Its enactment has changed the way historic resources on non-federal public lands in Texas have been managed ever since.

TexasGovernorPrestonSmithFormer Texas Governor Preston Smith
Link to original image here.

The wording of the original Code was fairly similar to a law that the State of Florida had in place at the time. The original Code allowed legal treasure hunting off the Texas coast, provided that the treasure salvage investigations were performed under the direction of a professional archeologist, and the State also got to decide which artifacts would be retained by the State. The Code also protected all publicly owned archeological resources in the state and it was and still is a very unique law that continues to be a model for other states. The Code was never intended to cover resources on private property without the expressed written consent of the private land owners, and there is no question that this aspect of the law will never change.

The original Code also created the concept of State Archeological Landmarks and a new state commission known as the Texas Antiquities Committee (TAC) whose job it was to administer the Code. From the beginning however, the staff of the Texas Historical Commission (THC) functioned as the staff of the TAC and the State Archeologist and Executive Director of the THC served on the TAC board.

The first archeological investigations performed under the jurisdiction of the Antiquities Code were performed by Dr. Frank Weir, head archeologist for the Texas Highway Department (currently known as the Texas Department of Transportation) in 1970. That same year, the San Antonio Missions were also designated as the first State Archeological Landmarks (SAL).

San-Antonio-Mission
Mission San Jose y San Miguel de Aguayo in San Antonio, Texas.
Link to original image here.

During the first 10 years after the creation of the Code approximately 250 permits were issued for archeological and historic structure investigations on public lands, and approximately 20 sites and buildings were designated as landmarks during this period. During the second decade, approximately 700 permits were issued and over 1500 sites and buildings were designated as landmarks.

The 68th Texas Legislature removed of treasure salvage provisions in 1983, and limits on the protection of historic buildings were added in 1987. Additionally, clarifications about the responsibilities of political subdivisions of the State were added in 1995. The Texas Antiquities Committee was dissolved in 1995, and the THC Commissioners took over direct administration of Code.

About the Author

Mark Denton is an Archaeologist, and Program Coordinator at the Texas Historical Commission in Austin, Texas.

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