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RESULTS
The full resolution 3D digital model is comprised of more than 1,000,000 poly-faces and over 500,000 vertices with a resolution (inter-vertex spacing) of 1.2 mm, and stored in Wavefront format (*.obj), which retains color surface mapping and the underlying mesh. The model in this format is approximately 145 MB (Appendix 2).
Comparison of Shuler's (1935) figure 1 with the 3D model provides a relative assessment of shape change in the track impression and indicates some erosion has occurred (Figure 6.1–6.3). In particular,
Shuler (1935, p. 10, figures 1, 2) described the bottom contour of the track [the heel of the track] as having a ~10 cm wide projection. Today the "projection" is eroded; leaving a more rounded posterior edge, which is now approximately 15 cm wide (Figure 5,
Figure 6.2–6.3,
Appendix 1). In addition, outer surface areas posterior to this edge have apparently fractured and fallen away (Figure 1.2).
The results of digital comparison of the 3D model with a synthetically altered version, demonstrates how weathering may be quantified in the future when a new set of scans are taken after the occurrence of natural erosion. The result of the deviation analysis (Figure 7.3) displays areas with zero deviation as yellow or cyan on the color map, while areas that vary from the baseline model appear as cool colors (negative deviations). Using commonly available software tools such as Rapidform, boolean subtraction of new scans from the baseline model yields volumes that can be used to quantify total volume loss, and point samples can be used to calculate the gap distance along normals between the two scan models (measurements in red boxes). In our example, the total volume change is 6,152.9 mm3 (Figure 7.3). The volume of loss can be produced as a 3D mesh and used to construct physical 3D models of "lost" volumes for restoration purposes.
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