A while ago, I was contacted by an Archeology student at Miami University of Oxford Ohio, who had some questions about using Meshlab to unroll some 3D scan data of a cylindrical object. She reference a great post at Meshlab Stuff on the subject but was having trouble implementing the procedure herself.
The scan data she sent me was of a South American ceramic cylinder stamp. According to the student, these cylinders were believed to have been used for marking cloth or skin. Further research on cylinder seals revealed that they were also used to mark clay. Unfortunately, as this group of scrolls are still being studied, I don’t really have much more information about this particular specimen.
So, like Indiana Jones researching an ancient civilization, I dug deep into the interwebs and came up with the following steps for unrolling a cylindrical surface in Meshlab. The 3D data she sent me was scanned using a high resolution 3D laser scanner.
- First, open up a new project and import the model (.stl, .ply, or .obj) using File > Import Mesh… The model she gave me came in with about 1.6 million faces, so I performed a Quadric Edge Collapse Decimation (Filters > Remeshing,Simplification, Reconstruction>Quadric Edge Decimation) to reduce it to a model of about 200,000 faces.
- Next, turn on the Axis View (Render>Show Axis) and show the Layer Window (View>Show Layer Dialogue)
- Next, watch this YouTube video, and use the Manipulators Tool to orient the model so that the axis you’d like to unroll is centered on the Y-axis.
Pressing the “x”, “y”, or “z” key will allow you to move the mesh or rotate it about that axis. Use the mouse to drag it into position. Align the axis you’d like to unroll with the Y-axis and make move the model so that one of the ends is positioned near zero.
- Lock the model in place by selecting Filters>Mesh Layer>Freeze Current Matrix and then clicking Apply.
- Use the Tape Measure tool to get the diameter of the object, and click to measure across.
- Use the Cylinder Unwrap Tool by selecting Filters>Smoothing,Fairing, and Deformation>Geometric Cylinder Unwrap and inputting the radius you measured in the last step. Click Apply.
- Done! Export the mesh and process the results!
Definitely a tricky process for those who are unfamiliar with the software or CAD in general.
Like Indiana Jones, my thirst for knowledge knows no bounds, so I decided to print the model I was given.
Then, I used some Sculpey clay I had lying around to create an imprint of the scroll. I totally felt like Indiana Jones uncovering some secret artifact. The image I was molded by an artisan many years ago in some ancient South American civilization. And yet I was able to produce the same imprint in clay over a thousand years later by communicating with someone I’ve never met over two thousand miles away via electronic mail to get a file containing an array of points in space created by 3D laser scanner and then printing the result in plastic… pretty cool.
Technology helping understand the past… awesome.