From Underground to Digital
The Xaghra Circle is the sacred site of the dead on the island of Gozo. A walled complex made of a number of natural caves which were adapted into a necropolis for the community that built the nearby megalithic temples of Ggantija and Santa Verna. The site was mainly in use around 3000 to 2400 BC, although the earliest tombs at the site date back to 4100 to 3800 BC.
The excavations at Xaghra have uncovered not just bones but also an extraordinary number of man-made objects. These important remains give us an important insight into the rituals and complex religious systems of prehistoric Malta. Amongst these artifacts are were a cache of 9 statuettes, found together in a heap on the floor at the Xagħra Circle. They are carved in limestone and it is likely that they were originally bound or wrapped together with perishable material such as animal skin. Although numerous statues were discovered from different temple sites in Malta, the human representations in this group are unique. Six stick human representations have been carved at different levels, from the roughest to the most complete and the decoration on the most finished two shows the same pleated skirts as those on statuary found in temples in Malta. Out of the other three small statuettes found bunched with these six, two of them have a human face whereas the third one looks very similar to one of the Għar Dalam phase animal heads.
This brief article describes the out first attempt at digitising replicas of these unique stone figures in preparation for a full digitisation process of the artifacts themselves in the coming months. Given that we were still experimenting with the methodology being used we preferred working with these accurate replicas rather than the original artifacts. Once digitised we wanted to create a brief animation showing the figurines from all angles. This methodology is split into three stages:
- Digital Acquisition using a 3D handheld scanner.
- Post Processing
- Replication 3D printing
Acquisition — 3D Handheld Scanner
The 9 Stone figurines were scanned using the newly acquired Creaform Go!SCAN 3D portable 3D scanner. Each figurine was scanned by itself, by placing it on a turntable with scanning targets placed on the turntable to ensure more accurate acquisition. The stone figure was scanned from two directions, facing upwards horizontally and facing downwards towards the turntable. Placing it on a turntable meant that the stone figure was safe and not handled unnecessarily. The figures were scanned in a 0.2mm resolution meaning that the distance between each scanned triangle was of that measure, this allowed maximum accuracy while also being able to scan the texture.
After scanning both sides of each figure, the meshes were cleaned in VXModel (a native application provided by Creaform) and merged to create one object for each stone figure.
3D Animation Creation Methodology
Exporting of data (Mesh/ Texture Data)
After the digital acquisition phase and cleaning in VXmodel, the data was exported. Such exported data includes mesh data and map data. Data which is exportable is the following;
- OBJ of the Mesh
- Diffuse Map (Colour Texture JPG/ PNG)
- Normal Map (To create a 3D texture JPG/PNG)
The above are the main important maps. Other alternative maps which would result in a better 3D visualisation of the model in the 3D software would be such as: Roughness Map, Displacement Map, Metalness Map etc.
3D Scene Set-Up
The next step was creating a scene environment of the 3D objects. The OBJ 3D model is imported and is oriented upright in the 3D Space. The mesh is then assigned a material in which the texture maps could be assigned. For this case just a diffuse map was assigned as a normal map was not needed due to the high sub division level of detail that there was on the model.
Lighting
A 3-point lighting system was then set-up in the scene. Such a system included
i. a backlight to give a sharp contrast on the back of the 3D object.
ii. a Front light to give a sharp contrast on the opposite side and
iii. a filler light is placed in front of the object in order to fill in any missing detail information on the 3D object. The Model is then 3D rendered using a real time IPR system in order to adjust the lights till the result seems to look visually pleasing.
Animating the figurines
After having the scene setup and all renders are looking good, the animation sequence can be planned out. In this case an animation of 12 shots was planned. 3 Shots to introduce the audience to what is to be shown and 9 shots consisting of a turntable for each stone figure.
Each mesh is keyframed for different movements. If the mesh is to make a rotation of 360 degrees and the animation is to last 5 seconds. That means it will require 25 frames per second multiplied by 5 which is 125. This the mesh needs to be keyframed at frame 1 at 0 degrees and keyframe at frame 125 at 360 degrees. It’s as simple as that. In the case of the turntable this exact method was used.
Post Production
After having the 3D mesh keyframed, the animation could then be rendered overnight, frame by frame. The Keyframes are then saved to a directory folder. The sequence of frames could then be imported into a post production software such as after effects. The animation could then be colour corrected, scaled and adjusted depending on what is required.
Video Production
After having all the shots corrected and rendered out, they could then be imported into a video software such as Premiere Pro. This will be in order to sort out the shots and connect the sequences together by also applying transitions to make the animation more professional and satisfying.
After compositing the video, the sequence could then be rendered and exported. A frame rate at 25 Frames per second was selected together with the desired export format in this case H.264.
The 3D model obtained from the scan was used to create .obj files which could easily be replicated on a 3D printer. Replicas with an accuracy of 0.2mm of the original scanned object were 3D printed using our resin printer as shown below. This process opens huge possibilities of replicating copies of artifacts, especially for educational purposes. It is our plan to create a library of digital twins of artifacts that can be downloaded by educators for 3D printing within schools.
Tony Cassar, Rakel Vella and Nicholas Vella Magri Demaio worked on this digitisation case study.
