Modelling Archaeological Collections
G Saravana Kumar
Sanjay G Dhande
Professor, CAD-P Laboratory,
Indian Institute of Technology,
Archaeological collections are vital elements that preserve the legacy and heritage of prehistory. The present work is a study carried out at Computer Aided Design Laboratory, Indian Institute of Technology, Kanpur (IITK) to record and archive morphological features of artifacts from past cultures.
The technology under study will allow archaeologists, researchers to view, analyze, and even reproduce artifacts in the absence of the original object. An ATOS II optical scanner digitizes the surface geometry of an artifact, the resulting data are stored as x, y, and z coordinate points and a connectivity list describes the relationship of the points to each other.
The scanned surface is represented digitally as a collection of tiny triangles. The result is a 3D digital model that can be viewed, analyzed, manufactured, and manipulated electronically. A complete archaeological monument could be scanned and a digital model created. This model can be placed on to 3D Digital Terrain Model (DTM) obtained form satellite imaging to yield a detailed 3D model of the archaeological site along with monuments.
Modelling art and archaeological forms
The role of the Computer Aided Design (CAD) in creating artistic shapes is an emerging trend. Integration of art and technology has not been realized and one reason could be that the needs and goals of artists are far less predictive and structured. Reverse Engineering (RE) can help a sculptor to convert his physical creation into a digital form. The form thus captured can form a digital museum and one can manufacture the sculptor’s creation at any time through rapid prototyping (RP). Scaling up of models in digital domain is easy and thus a sculptor can make a small model and scan it and later make a physical instance of any size either through RP or CNC machining. A summary of session on Art and Rapid Prototyping is given by Michael Rees  and he discusses the concept of integration of art and science and its implications. A foreword to CAD journal by Se’quin  is again a thought provoking article.
On the one hand the scope lies in creating new design tools for sculptors and on the other the scope lies in creating tools for modeling and manipulating archaeological collections and heritage artifacts digitally. Reconstruction of fossils, archaeological collections from fragmentary material requires morphological and artistic talents and is a modeling intensive task. Three dimensional graphical reconstruction and creation of physical models from this representation enable researchers to do their work more accurately without damaging the original artifact, which is not the case with traditional methods of reconstruction. Guangming Zhang et. al.  had done a work on reconstruction of Homunculus’s skull by rapid prototyping. A technical note by D’Urso et. al.  describes RP for biomodeling in palaeontology. The present study is a demonstration of the application of RE and RP in archaeological modeling and heritage preservation.
Fig. 1. The sculpture of Hanuman idol
Reverse engineering (RE) and rapid prototyping (RP) are emerging technologies that have been accepted to play a promising role as a data acquisition and form realization tool for free form sculpted surfaces. RE refers to the process acquiring point data from the surface of the part using a scanning or measurement device and creates a digital model of the same. In recent years, laser scanning has become a powerful tool in capturing the geometry of complicated models. The Computer Aided Design (CAD) model developed by an RE process can be converted into a physical prototype using an RP technique. Generally, in RP, prototypes are fabricated layer by layer. It uses additive manufacturing processes, which do not require any tools or setups compared to the subtractive techniques used in the traditional machining. Different fabrication methods exist for RP, but nearly all use the same geometry input format, called STL (Stereo Lithography), which consists of a list of triangular facet data.
Fig. 2. The point cloud and STL model of the digitized idol
The main RP source at IITK is a Fused Deposition Modeling system (FDM) RP system  at Computer Aided Design Lab (CAD Lab) a central facility of the institution. The system is Stratasys FDM 1650, equipped for prototyping with ABS plastic. For data acquisition for RE at CAD Lab, a ATOS II optical scanner  is used. The main computer facility for RP at CAD Lab are two Silicon Graphics on Irix platform, several PC with 512 MB RAM and 40 GB local disks.
Fig. 3. The RP model
A digitising exercise of a Hanuman idol carved from a rock slab was taken up. An ATOS II optical scanner was used to digitize the sculpture. Optical scanners have a high rate of digitizing and are non-contact and these are the essential advantages of using them for scanning large stone monuments. Fig. 1 shows the idol chosen for scanning.
The idol’s gross dimensions are ~ 1 ¼ ft X 2 ½ ft X ½ ft. The time taken to scan the idol was approximately an hour. The point cloud was then sampled based on curvature to approximately 1,30000 points. The point density has to be fixed according to the size of the object and the intricacy of features. The point data was then processed to yield connectivity list file that described the relationship of the points to each other. The output of the processing is a STL file that consists of a list of triangular facet data.
The time to process the data was 25 minutes on a PIII, 1GB RAM UNIX Workstation. The critical issue here is the requirement of computers with high-speed processing and large memory for real time handling of huge point cloud data. The point cloud and the STL file of the Hanuman idol are shown in Fig. 2.
The digital model thus created can be used for viewing, dimensional and mass property evaluation and surface feature analysis to name a few. Reproduction of the artifact from its digital representation through RP or conventional CNC machining is readily feasible. The STL file of the Hanuman idol was used to reconstruct the same through the FDM RP system in the Lab. A half-size scaled model was fabricated. The fabricated physical model is shown in Fig. 3.
The model of the artifact made by RP presents a new effort in bringing information-based manufacturing technology for archaeological studies. The accuracy and reproducibility of the models provide archaeologists and scientists with a better way to preserve artifacts and a more durable, yet tangible subject to study.
A complete archaeological monument could be scanned and a digital model created. This model can be placed on to 3D Digital Terrain Model (DTM) obtained form satellite imaging to yield a detailed 3D model of the archaeological site along with monuments.
The work on these lines is in progress at our lab. Reverse Engineering of physical objects to obtain three-dimensional geometrical models and physical realization of these models through rapid prototyping is a fast developing technology in which interest is currently high. The present study has demonstrated the application of data acquisition through RE and form realisation through RP for modeling archaeological collections.
India is bestowed with many instances of human creation from various ages in the form of temple monuments and other artifacts. Though these forms of art have survived test of the time but many have been destroyed by natural calamities or man-made disasters in the form of war and terrorism. The authors hope that the present study will pave a way towards digital preservation of these invaluable and unique artifacts.
- Michel Rees, Rapid Prototyping and Art, Rapid Prototyping Journal, 1999, Vol. 5, No. 4, pp. 154-160.
- Se’aquin C.H., CAD and the Arts, Computer-Aided Design, 2001, Vol. 33, pp. 345-348.
- Guangming Zhang, Yi-Chien Tsou and Alfred Rosenberge L., Reconstruction of the Homunculus Skull using a Combined Scanning and Sterolithography Process, Rapid Prototyping Journal, 2000, Vol. 6, No. 4, pp. 267-275.
- D’Urso P.S. Thompson R.G. and Earwaker W.J., Stereolithographic (SL) Biomodelling in Palaeontology: A Technical Note, Rapid Prototyping Jour., 2000, Vol. 6, No. 3, pp. 212-215.
- Stratasys Inc., https://www.stratasys.com.
- GOM mbH, Braunschweig, Germany, https://www.gom.com