In this article, we explain you the techniques that are using the most advanced museums to create three-dimensional models of monuments and objects, and the unexpected possibilities that these technologies open
What is a 3D model?
The best way to find out how it works is through 'hands on' experience. Here at the side, there is a 3D model of a patera, a shallow dish for ritual offerings. Click on 'Play' and wait for it to load. You can use the mouse to turn it in every direction and you can see it from all sides, along with all its features. You could say it is a digital model of the object. In the field of cultural heritage these three-dimensional representations can be as small as a Roman earring, or as large as a mediaeval monastery.
These models can be made in two ways: - Directly from the real object using image capture technologies such as photogrammetry or volume capturing techniques such as 3D scanning. - Direct modelling using a 3D design program.
Photogrammetry: the production of 3D models from photographs
Photogrammetry consists of making 3D models from photographs. The photographs are taken in such a way that the images can later be superimposed on each other. A specialised program processes the images, finds coincident points, and then calculates their location in three-dimensional space to produce a point cloud, which reproduces the shape of the original object. If these points are joined with lines, a network of triangles, or mesh, is created, on the surface of which it is possible to add the colours and textures captured in the photographs. The 3D model has now been created. At the present time the most frequently used photogrammetry programs are Metashape and ReallityCapture.
3D scanner, registering position points
3D scanners register position points using laser beams, in the case of laser scanners or, in the case of structured-light 3D scanners, by means of projecting stripes of white light.
The laser scanner works by firing a laser beam at the surface of an object, which is then sent back to the device in such a way that the position of the point of impact is registered. An extremely precise three-dimensional image of the scanned object's shape is produced by the automatic repetition of this procedure over every few millimetres of the object's surface. This information is then processed, using programs such as Leica Cyclone, Scene or ReCap, to produce a point cloud which, as with photogrammetry, enables three-dimensional models to be created.
Sometimes, programs such as Meshlab are used to build the mesh in a more controlled way. Structured-light 3D scanners do not use laser beams, but rather stripes of white light. The device registers the deformations of these stripes on the surface of the object to produce a point cloud using its own software.
3D design, modelling digital objects
The technique used to create digital objects from modelling is 3D design. This technique makes it possible to digitally draw or sculpt a 3D model. Since it is created from scratch, it can be very true to life or, on the contrary, it can be a completely new creation.
Once the shape has been created with a mesh, the procedure is very similar and textures, which can either be captured from the real world or invented, can be added.
3D models have been used for many years for special effects in cinema and 3D videogames. They have also been used in cultural heritage for decades, but only very occasionally. Over recent years, however, technical advances have been such that many institutions, and people working in the field of cultural heritage, now have this technology within reach. With it they can perfect some of their previous procedures and they can also use it to explore completely new avenues. Here are some examples.
Restoration/conservation: In the field of restoration the use of 3D models can detect deterioration and deformations that would otherwise be invisible. It can also be used to create a register of these flaws over time by capturing data at regular intervals. In the case of fragmented works, it makes it possible to study the way in which the fragments fit together, without having to touch them, and it also makes it possible to create moulds of the missing pieces, or supports which are perfectly adapted to the pieces themselves.
Documentation: For years the documentation accompanying elements of cultural heritage, especially buildings, has been produced with the use of photography and plans. In a few years' time, it will be difficult to find documentary databases without 3D models because they constitute an integrated registry of information, and they provide a visualisation that is much closer to reality. In the case of buildings at risk, or in areas of conflict, detailed documentation such as this can be a very useful tool for use in partial or total reconstruction.
Research: When we publish a 3D model of a Baroque sculpture or a prehistoric axe, we are placing a very valuable resource at the disposal of researchers throughout the world. To be able to see the object from all points of view, to be able to amplify the image, and even change the position of the light source illuminating it in order to find irregularities on its surface, is almost like having the original object in one's hand. In some cases it will continue to be essential for researchers to take a journey to check some detail in situ, but they will know exactly what to expect from the original.
Dissemination: The ability we now have to show three-dimensional objects via the Internet on any device, including tablets and mobile phones, means that we can reach a very wide public and make cultural heritage more accessible to a younger audience. 3D models also open up new possibilities for communication, such as Augmented Reality, in which the object appears on screen, integrated into the environment being captured by the camera of a mobile phone, or Virtual Reality whereby, with some simple cardboard VR glasses, it is possible to see the object in three dimensions in a completely realistic way.
Where can I find all this?
Would you like to see what we have been describing here for yourself? You can start by exploring the most well-known online cultural heritage resource: Sketchfab. It is the YouTube for 3D models. It works in a very similar way. You can see models, but you can also open an account and upload your own. Or you can create galleries of the models you most like.
3DHop, on the other hand, is a 3D model viewer developed by a research group and intended especially for museums and heritage institutions. You can see some examples of the way it is used in their gallery section.
Success stories
The use of 3D in the field of cultural heritage has given rise to some very interesting proposals. The Smithsonian Institution is probably the first cultural institution to have embarked on the mass scanning of its collections. The British Museum's gallery on Sketchfab has more than 10,000 followers, which is not surprising given the quantity and quality of its objects and virtual models. In Catalonia the Museu d'Arqueologia de Catalunya has been a pioneer and has an excellent selection of objects.
Vilamuseu is a special case in that it prints 3D models of objects in its collection in order to reach, through the sense of touch, an visually impaired audience. With regard to endangered heritage there are several initiatives, such as CyArk, Rekrei and others, that document heritage that is at risk for various reasons, be it armed conflict, or the risk of natural disasters.
In the case of Ullastret 3D, all the scientific and archaeological knowledge about this Iberian settlement was incorporated into a 3D model. The virtual reconstruction has been used to create photographs, videos and immersive experiences to make all this knowledge more accessible to the public at large, and do so in a very attractive way. For the exhibition Re-descobrint Centcelles, the National Archaeological Museum of Tarragona (MNAT) applied these technologies to present the latest proposal for the architectural reconstruction of the Roman Villa in Centcelles, combining photogrammetry with the 3D reconstruction of the building. In Empúries they have also used 3D technology to virtually reconstruct a Roman house, the Domus dels Mosaics.
