Wadi Farasa, Petra – Taking the Lesser Travelled Path

An average of 2000 visitors invade the principal valley of Wadi Musa in Petra, Jordan every day and one would think it impossible to find places of solitude and tranquility and a sense of immersion into the past. But then there is Wadi Farasa, a small valley bordering on Wadi Musa in the in the Petra Archaeological Park. Working in places like this makes one forget all the practical difficulties and technical complexities of scanning and documenting heritage sites.

Wadi Farasa, physically accessible only to those with a penchant for adventure and discovery, can be reached by three main routes, all of which require some physical effort, especially when carrying laser scanners, RTK GPS, tripods, cameras and whatever else a surveyor needs to survive a day in the field. As a UNESCO, ISPRA, PAP and DOA partner in the Petra Siq Stability Project (Lidar News, Vol3 No3), the Zamani team was tasked with the scanning and documentation of the principal Nabataean and Roman monuments in both Wadi Musa and Farasa.

There are numerous tombs, altars and other rock hewn structures in Farasa, outstanding among these are the rarely visited, fascinating “Roman Soldier’s Tomb” with its elaborate façade, the “Coloured Triclinium”, a banqueting hall with its, for Petra standards, elaborate interior cut out of the rock and the “Garden Tomb”. However rewarding and exciting it was to scan the main monuments in Farasa the team left the valley with a sense of frustration when, due to limited resources, so much had to remain unrecorded in the face of threatening deterioration through natural and manmade phenomena.

Of interest in this context and especially from an engineering perspective is the threat posed to the tomb facades through rain water. The Nabataeans designed an effective and sophisticated system of water channels preventing rainwater from draining over the facades. This system has become dysfunctional over the centuries and needs resurrection, where metrically accurate spatial documentation can be great value.

Anybody who has laser scanned will be aware of the scan-hole phenomenon, the impossibility to scan every single part of a complex building without leaving some places un-scanned. Photogrammetry and especially Structure-from-Motion and handheld scanning can fill many of these gaps, but there will always be something left unrecorded.

The easy way out is offered by well-established hole-filling algorithms, however this is not acceptable when documenting heritage for reconstruction conservation or as a scientific record as was required in Petra.  In heritage documentation there will always have to be a choice between the aesthetics of appearance and faithfulness.

When scanning the natural rock formations surrounding the monuments of Petra for a Virtual World, the scan holes took on an even ‘larger dimension’. While the need for extreme faithful recording did not arise for the landscape model, the presence of gaps in the model surface had to be addressed in the creation of the virtual world.  As Virtual Tourists can roam a Virtual World at will, they are likely to ’fall’ through scan holes or encounter ugly, unnatural-looking places resulting from surface filling algorithms. In the present Virtual World produced by the Zamani project the latter was adopted.

Unfortunately, no permit to fly a UAV in Petra could be obtained by the Zamani team. Aerial vertical and oblique photography is planned for future modelling of the landscape. However, full cover will be even more difficult to achieve as in the case of the monuments and it can be said with some certainly that, depending on scale, a complete model will not be possible.

To document Wadi Farasa scans were acquired with a Z+F Imager 5010 and full dome panoramas as well as images for photogrammetric processing were captured. The laser scanning while largely a routine operation, required on occasions daring mountaineering by the team complicated by the nightmarish thought of possibly dropping a scanner while scrambling to exposed rock perches. A 3D model of Wadi Farasa and a Virtual World resulting from this campaign are partially accessible on the Zamani web page.

The memory of Petra, with its fascinating monuments, its awe-inspiring natural beauty and its biblical atmosphere, which is even more apparent in Wadi Farasa than anywhere else in Petra stays with the visitor forever. This timeless ‘Red Rose’ city leaves one with a sense of longing to come back again and again. The Zamani Project is grateful for having been given the opportunity to work in and be part of this unique heritage site, which needs to be preserved – at all costs. The Zamani project is now attempting to find funds to continue documenting more of the over thousand tombs of Petra.