3D-scanning in the jungle

Cave entrance seen from first chamber

At the end of May I went to Belize to work at a Maya site out in the jungle for three weeks. The site, originally referred as “Awe Caves”, is a medium-sized Maya ceremonial center located in the western part of Belize. It is of particular interest because a large cave with an extensive dark zone tunnel system resides directly beneath the largest temple in the site core. The project of 3D documentation and reconstruction of this site is part of a larger research project of preliminary investigation started in the summer 2011 and directed by Holley Moyes, UC Merced. The first year some 3D documentation of the excavations was done by Fabrizio Galeazzi, UC Merced. This year one of the ambitions was to 3D-scan the complete cave. The cave is a natural geological structure, but has been divided into nine chambers in succession, by the Mayan people. The cave turns around so that the last chamber enters into the first, about 10-15 meters up on one of the walls in the entrance chamber. The different division of the chambers varies from clearly manmade structures to more or less natural boundaries.

Snapshot from pointscloud. The colored area shows a manmade wall

The 3d scanning was done with a Faro Focus 3D scanner. It is a small and compact scanner, that is easy to carry and has everything needed to scan built in. Faro Focus 3D including tripod, weighs about 8 kg and is therefore the ideal scanner for a mission of this kind. One important benefit from the small format of the scanner is evident in the fact that the scanning of the complete cave were made in just eight days.

Scanning of excavtion in the cave was done with light

Right from the beginning it was decided not to try to capture color information in the cave, but only settle for the geometry. To capture color information would demand large amounts of lights to illuminate the cave properly. Bringing enough lights and spending time placing them as good as possible would have been a huge and costly task far beyond the scope of the project.

At the start of the campaign, a fairly normal scanning strategy for larger structures was applied. This was a relatively efficient approach in the entrance chamber, but further into the cave it got more and more difficult. With such an extremely irregular geometric structure found in the cave, the risk to miss important parts was much larger than usual. So after a few days the scanning strategy significantly changed and scanning positions were moved closer together to be sure to cover as much as possible. It culminated in the fifth chamber, which was a complete jumble of rocks, stalactites, stalagmites, narrow cavities and hidden structures. This complex geometry led to a scanning strategy, in which the different scan positions were placed only a few meters from each other. This of course gave us a huge amount of scans that, at this writing, still isn’t fully post processed. 

The humidity caused other problems as well

Another objective of the scanning campaign was to verify how well the scanner handled the very special climate prevailing in a place like this. This is subtropical jungle and the work were made during a time of year when it was quite a lot of rain, high humidity and relatively warm. Inside the cave the temperature was slightly lower, but the humidity was significant. Anyone who has worked with electrical equipment in these conditions can tell you that humidity plays tricks with equipment that does not occur in dryer environments. 

Scanning part of the entrance from a spot in the jungle

We were pleased to see that the scanner handled these conditions well for most of the time. The battery ran out faster than usual, but that was expected. The only problem experienced was that the touch panel of the scanner stopped working on a number of occasions. The touch panel is mainly used to adjust the settings for the different scans, such as resolution or whether the scan should be done with color or not. Once these settings are made, the need to use the touch panel is not that big, with the very important exception of starting each new scan. Hence a non-functioning touch screen could be a serious problem. Fortunately, the scanner also provides a more stable button under the touch screen, which can be used just to start scans if you cannot start them otherwise. That saved a lot of time, since the only way to get the touchscreen to work again was to turn the scanner off and let it rest for a couple of hours. To prevent problems with humidity, the scanner bag was equipped with several small bags of silica gel during the entire period in Belize. It is used as a desiccant to control local humidity and may have done some good in keeping the scanner in such a good shape.

All in all it was a very interesting trip and we are really looking forward to have time to work with the data.

Scan of the entrancecave. To the left of the middle you can see two people that happened to be scanned. Good to use as a reference

/Stefan

CENCELLE

I just come back from a very short archaeological mission in Cencelle (figure 1), where  together with  Stefan Lindgren and Doriana De Padova we joined the excavation team leaded by the Prof. Francesca Romana Stasolla, and her collaborators: Dr. Sergio Del Ferro, Dr. Lorenzo De Lellis and Dr. Lara Tonizzo Feligioni. 

Figure 1 Archaeological excavation of Cencelle, Tarquinia

Cencelle is a middle age town founded by Leone IV during the IX century with the aim to provide a safe refugee to the inhabitants of Centumcelle (Civitavecchia). 

Centumcelle  was an ancient  town  along the costs few miles north of Rome, which in that period was constantly under the attack of the Saracens.  Cencelle is  amazing, the landscape is beautiful and the site incredibly rich. 

The excavation is under the scientific direction of the University of Rome "La Sapienza", that together with l'École française di Roma, started the excavation in the 1994.  Goals during our short permanence there were: the documentation of structures no more under archaeological investigations using the laser scanner, the use of Image based modeling techniques for the documentation of the ongoing excavation (cemetery), the use of the GPS to map the site.

Our work was mainly focused on finding a work methodology  that could have been  easily integrated with the current system of documentation in use in Cencelle.

As previously explained, we decided to employ the Laser only for the structures that were no more under investigation, in fact, despite the efficiency of the scanner in providing resolute, accurate and precise 3D models, the time  required for the  data post processing would have been not sustainable.

Figure 2 Map site realized using the RTK GPS

Despite some problem with the vegetation... in two days we handled to finish the work with the scanner acquiring material that will be used in the coming months  by Doriana De Padova to highlight aspects of these structures not jet studied before.  At the same time, with the help of the students we started the documentation campaign of the ongoing excavation of the cemetery in order to provide material that (we hope) will help the excavation team to have a better view of the complicated relations between the different graves currently under investigation.

Detail of the cemetery, 3D model of one of the burials processed in Photoscan and visualized inMeshLab

Once again the use of this technique have been incredibly efficient, already the first day it was possible to produce dense and detailed models able to provide an extraordinary view of the spacial relations between the different features of the area under investigation.
Differently from a normal  raster images or vector file, the use of 3D models provide an impressive view of the ongoing situation that can provide different perspectives, already  during the excavation campaign or even after the end of the investigation. The GPS has been used to produce a quick description of the topography of the site, moreover this instrument allowed to calculate the position of Control points that will be used to geo-reference the 3d models coming from the different technologies employed during this archaeological campaign.

3D model of the cemetery processed using  Photoscan and visualized in MeshLab

3D model of the cemetery processed using Photoscan and visualized in MeshLab

3D model of the cemetery processed using  Photoscan and visualized in MeshLab

/n