By Vladimir Vilde
Once a heritage site is lost, only textual descriptions, drawings and occasionally photographs remain. Nowadays, 3D models play an increasing role as a visualisation medium. They can provide an immersive experience that reflects the original appearance of a site . Since these models are born and stored digitally, they can include metadata that enhances historical information and adapts the model to different uses.
The creation of digital surrogates of lost heritage through 3D imaging is not a recent development. Since the beginning of 3D creation software, designers were inspired by ancient sites with various purposes. In recent times, however, due to the fast technological development and the increase of current conflicts threating heritage globally, 3D surrogates have taken on a more “protective” and political aspect.
Photogrammetry is a very interesting way to produce a 3D model using 2D pictures . This technique has risen in popularity due to increase of accessible cameras by the public and efficient software to processes the 3D models. Photogrammetry is now well known and plenty of models are made for heritage, even to the point where we can actually 3D print surrogates of famous statues. However, other challenges arise when heritage that has already been lost, mainly due to the limitation to existing pictures and to the causes behind the destruction. The three main challenges could be summarised as follows:
In order to create a digital surrogate from existing images, we must have as much information as possible. We need mages from different views and ideally from all around the object of interest. The number of pictures available is often not enough for a full 3D reconstruction using photogrammetry. When relying of images from tourists, details are generally missing such as the back of statues. Therefore, additional processes have to be considered such as image processing or manual modelling (respectively before and after photogrammetry process).
This process becomes very challenging when the pictures are in terrible conditions (or old). Image processing for heritage is hugely exploited but current practices are mostly based on a controlled acquisition. Research has to be undertaken in order to improve the condition of damaged pictures to enhance the resulting photogrammetry model [Fig. 1].
One clear example is light exposition. Pictures were taken at different times resulting on a complete inhomogeneity of the colour intensity for the same object. This problem is reduced in a museum, but still exists due to the different camera setup.
Collecting photographs from the past requires a good organisation and a strong network of volunteers. In most cases, local academics, neighbours, tourists or even army officers have to be contacted. Without organisation and communication, the efforts are overlapping, volunteers eventually end up asking the same people and facing the same difficulties. Two different approaches can be considered:
- Individual / crowdsourcing (ex. Palmyra Photogrammetry )
- Public engagement/ citizen science (ex. ProjectMosul )
The first is based on an individual project that asks for others to contribute by providing photographs from tourists or researchers. It is efficient with a good network but does not include external members which limit the outputs and applicability. Participation in the second approach is open to everyone, from collecting sources to processing models, but can be hard to organise. Communication is challenging due to the diversified interests, time commitments and location of volunteers.
3D models have usually a specific purpose, but can be reused in many ways thanks to the strong appeal to the public. Many digital surrogates currently shared worldwide seem to be famous less for their historical value than for who destroyed it. If this is true, it would mean that 3D models are used as a political tool, rather than educational. There is some proof to this statement: for example, the models from Yemen are largely unnoticed, in parallel with the low public profile of Yemen’s conflict. World heritage sites are destroyed, models and pictures are presented, but little is said about it. Meanwhile many projects that focused on sites connected to Daesh’s destructions became well known within a few weeks. Additionally, the real status of artefacts is sometime wrongly acknowledged: the museum of Mosul is often stated as “destroyed” . In fact, only a part of it was displayed during the video of Daesh and therefore destroyed: the fate of the rest is still unknown.
An important question arises when our goal is to digitalise lost heritage: Shall we produce models of what is supposed to be lost but could be untouched or even worst, looted? The last point is not negligible since spreading a visual of looted artefact among the public may reduce its chance to be found again.
But another question must be asked: “Which state of the artefact has to be digitally reproduced?” Indeed, Daesh didn’t invent neither looting nor destruction of cultural heritage. The Northeastern palace of Nimrud [Fig. 2] was already in terrible state before Daesh wiped it out. We have to be aware that Iraq went through several wars across a few decades. A looted Lamassu’s head (from 2008)  was found by the US and there is even record of loots during the 19th century after the discovery of Nimrud . Showing involvement in cultural destruction by different countries or groups is not out of consideration. After all it is probably why Yemen is unnoticed: Western countries are involved in trades of bombs that fall on archaeological sites and museums.
The challenges to the digital reconstruction of lost heritage are not limited to technical aspects. They also include social, political and legal issues, since it is a topic that motivates great public and political interest. The responsibility of what is communicated should be considered alongside the fact that heritage destruction is not restricted to a geographical area or a particular group.
 http://www.slate.com/blogs/future_tense/2016/01/27/_3d_scanning_lets_historians_digitally_ preserve_cultural_artifacts_threatened.html?platform=hootsuite
 Oates, J., & Oates, D. (2001). Nimrud: An Assyrian imperial city revealed. British School of Archaeology in.