Typically, virtual 3D reconstruction is used for archaeological sites or ruined monuments, where little is left to imagine what has been at a certain site in the past. In the open air museum Raversyde Atlantikwall however, the situation is different. A battery unit of the German coastal defense, called Aachen, was not only preserved after the first World War but was also reused by the German army in the second World War, and preserved after that war too, making it impossible to restore the WW I remains without touching the WW II remains. So virtual reconstruction has a triple goal here: visualising the extant remains in their WW I state, showing the many WW I elements that are not preserved today and showing the evolution that the battery went through during the war.
Our virtual 3D reconstruction is based upon five types of sources: aerial photography, photography on the terrain, photographs of similar batteries, written sources and the extant remains. Let’s start with aerial photography. Airplanes were brand new in 1914, the first successful flight only happened in 1904. By 1912, planes were build for military use, in fact, most of the early production of airplanes was destined at military goals. One of them was aerial photography, so by 1915 we have reconnaissance flights that depict Battery Aachen regularly. During the war, the battery was photographed regularly from the air, so we can observe the changes that happened over the period 1915-1918, only limited by the quality and detail of the different aerial photographs.
A second source are the terrestrial photographs taken on the terrain by soldiers and the military PR units. These photographs show a wide range of subjects and areas and provide a lot of essential detail for the virtual reconstruction, as long as the photographed area can be identified. Also photographs taken by Belgian soldiers in 1918, when the abandoned battery was taken, were very useful.
When interpreting the aerial and terrestrial photographs, it is very useful to have additional photographs of the housing and and equipment of similar batteries. For example, as we did not have plans of the cannons, we used additional photographs of the same cannons in other batteries.
A major element of the virtual reconstruction is functional analysis: we try to understand how the battery functioned and which role each of the identified elements had. In this analysis, additional written sources are very useful. We used for example spy reports that described the battery and its operations but also plans of the bomb elevator that brought projectiles from the storage bunker onto the cannon platform.
All bunker and cannon platform remains were measured outside and inside and analysed to distinguish between the different phases during the first WW and the later additions of the second WW.
Based on the plan and terrain model of today, we identified all man made structures on the aerial orthophotomap and estimated sizes and integration in the landscape. This is far from trivial as the quality of the aerial photography was substantially lower than today.
Based on all these sources, we created a virtual reconstruction for the newly build battery Aachen around May 1915 and for 1917, showing the changes and reinforcements made after the bombardments by the British Navy in October 1915. Many dimensions and materials were derived (or sometimes guessed) from the photographic material and the length of shadows on the aerial photos.
In this way, many elements in the current archaeological park can be linked to old photographs and visualised in 1915 and 1917 by the virtual reconstructions.