03-12-2012, 02:35 PM
Use of Hand-held Laser Scanning and 3D Printing for Creation of a Museum Exhibit.
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Abstract
Biological anthropology as a discipline continues to be holistic in both its approaches to
understanding research problems and its borrowing of methods from many related disciplines. More
and more, digital imaging is becoming an integral part of data acquisition and analysis in biological
anthropological research. With many new emerging technologies, however, these techniques are
also now contributing even more to research dissemination. One of the newest tools in
anthropological research is 3D object printing. Stereolithography has seen limited use, but the costs
are often prohibitive. New developments in 3D object printing have begun to make this technology
more available to osteological studies. Here we discuss the use of 3D laser scanning and 3D
printing to re-create human skeletal remains for a museum exhibit. A Polhemus 3D laser scanner is
used to capture the geometry and shape of the individual bones. The point clouds are then edited and
exported as STL files for printing on a Z-Corp Z406 3D printer. The recreated bones are then
incorporated into the exhibit, yielding an accurate and realistic depiction of the original skeleton.
An overview of the challenges associated with the project and its successful completion are
discussed in the context of the role of 3D printing in bioarchaeological research.
Introduction
New technologies allow researchers in anthropology to
overcome some of the challenges of working with ancient
human remains. Virtual archaeology, including 3D visualization
and modeling, is rapidly becoming integrated into
the mainstream dissemination of archaeological research
[Weber 2001; Weber et al. 2001; Zollikofer and Ponce de
Leon 2005]. Additionally, these new methods are helping
to improve communication between researchers and the
public.
In 2005 the Mennonite Heritage Village (Manitoba, Canada)
opened a new museum exhibit on the ‘Funeral as a
Rite of Passage’ in Mennonite communities. The exhibit
was to include a display presenting an archaeologically
recovered human burial of a Russian Mennonite woman
who lived in the late 1800s and early 1900s in the former
Schoenfeld village in southeastern Manitoba. Due to the
culturally sensitive nature of the display of human remains,
a replica of the skeleton was created for the exhibit. A
non-invasive method to replicate the remains was employed
in order to avoid unnecessary damage. This paper
presents an overview of the challenges encountered in
successfully creating the replica using a hand-held laser
scanner and 3D printer.
Laser Scanning
The shape and geometry of the human skeletal remains
was acquired using the Polhemus Fastscan handheld 3D
scanner. The scanner uses a laser, camera and motiontracking
system to accurately record a 3D point-set of the
original object surface. The laser and range-finding camera
are contained in a portable handheld wand (Figure 1).
Image Processing
Image processing of the scan data was undertaken using
RapidForm software by Inus Technology Inc. Multiple
scans of objects were registered to create 3D models of
each skeletal element. STL files are easier to register since
the format gives a visually understandable surface for the
registration process. Using point files often leads to picking
the wrong points since the depth cues are not as visually
apparent. The editing process followed a specific
pattern: Registration, Simplification, Detailing and Cleaning.
Registration
The individual scans were registered using the “Initial
Registration” command in RapidForm. This command
requires the user to input three or more points in common
between the two scans, and matches the scans using the
curve equations between the similar areas as landmarks for
the registration process. It is important to include a recognisable
common area between the scans for registration.
The fine register command was then executed to increase
the accuracy of the registration process. The initial registration
yields an effective averaging of common surfaces,
but the fine registration matches the scans more accurately.
Simplification and Detailing
The simplification process is necessary for accurate, clean
model files. Since skeletal material has a very complex
surface morphology, it can be difficult to produce an accurate
clean model using standard procedures. The new
registered STL file is exported to the proprietary Rapid-
Form point file (.pts). This file is then reloaded under a
new project window. An exact copy of the point cloud is
made and reduced several times and re-triangulated. The
surface of the reduced point cloud is therefore very simple
and represents the basic shape of the original, while reducing
the number of boundaries and incorrect normals. Incorrect
normals and excessive boundaries develop from
errors in the triangulation process with complex objects
such as bone. The simplified surface is then fit to the
original high detail point cloud. This brings out the surface
detail by increasing the triangle data without introducing
new boundaries. This process produces a detailed
and accurate representation of the original object without
errors and unwanted holes. RapidForm recommends this
approach when generating complex surfaces from point
data in the help manual for the software.
Cleaning
The last step for each 3D model is to double check that
the model is free of errors and a manageable size. The
detailing process can add a significant amount of triangles,
producing an excessively large file. The decimate function
reduces the number of triangles at a minor cost to the
amount of surface detail. This function is applied during
this final step along with the clean function to double
check the absence of crossing faces, bad normals and nonmanifold
faces. These along with excessive boundaries
can cause problems with the physical model when the STL
file is printed.
3D Printing
The virtual models were then printed using a Z-Corp Z-
406 3D printer. This printer is capable of printing in both
colour and monochrome, but was restricted to monochrome
for this project. This printer uses plaster-based
material and binder solution to recreate 3D objects. A
layer of plaster is first spread onto the build chamber floor.
Conclusions
This paper has presented a project which describes the
replication of human skeletal remains using a hand-held
laser scanner and 3D printer for use in a museum exhibit.
A variety of technical challenges were addressed, and this
project demonstrates that the use of these technologies is
both practical and economical for public presentation.
Ultimately, however, the success of this project is in the
experience that museum visitors take with them.