Tas Silg Temple

We had an incredible opportunity to access an archeological site restricted to the public to investigate the cisterns on site. The temple has a great deal of history... from being a pre-historic site of worship, to a Roman temple that stood as a beacon from the bay below. One interesting feature of the temple was the clay walkway that surrounded the center of the temple (only about half still in tact) that was patterned with evenly-spaced square pieces of marble. Our archeologist on site, David, said that this was a way of defining a "medium" for extremely important ground and common ground. It was a mix, making it a sort of semi-formal site. The temple was of course in ruins above ground, but was currently being excavated for further discoveries in the area. There was a full-immersion baptism site, signs of large columns to hold the roof, and clear signs of divisions within the temple.

The cisterns, however, we more intact underground than the remains above ground. The first cistern was square with 4 hallways in each direction. One was too shallow to investigate, and was even hardly noticeable, as the water level only allowed us to see the slit of the bottom of the hallway. The other three hallways led to large rooms filled with rubble. Each of these rooms had at least two off-shoots that showed signs of even more caves. Unfortunately, all of these accesses were too shallow for the ROV to pass.

The second cistern was similar, but only one hallway was deep enough to explore. This hallway was back towards the first cistern. Once we reached the end of the hallway, it was clear that this hallway connected the two. Below, you can see the mosaic of the sonar images we gathered from the cistern. As you can see, this was a very complex and exciting cistern.

We explored one more cistern out in a nearby field, but it was only a circular well with no outlets. Below is the group with our archeologist, David, at the temple site.

Mdina Archives 3D Cistern Visualization

On Wednesday (3/16/11), we went to Mdina to explore another cistern at The Archives of the Cathedral of Malta. This cistern was especially interesting because of its shape. The cistern consisted of a shaft down the center and two bell-shaped cisterns branching off. The smaller cistern's access point was at about 16 meters underwater down the shaft, while the larger cistern's access point was at about 22 meters down the shaft. Gathering enough sonar data for this cistern was very difficult due to the complexity of two cisterns in one. It was difficult to navigate between cisterns through the shaft while keeping track of the distance moved and the orientation of the ROV. We collected 50 sonar scans in all where 15 of them where side-scans. (The sonar was rotated sideways to collect vertical data of the cisterns).

Over the past few days, Chris and I have been analyzing this data and creating sonar mosaics (the compilation of multiple sonar scans to create a map) in order to create a 3D map of the entire cistern. So far, we have created a 3D map and now I am handing it off to Christina for her to transform it into a pretty 3D visualization. The image below represents a map of the entire cistern, which includes both of the sub-cisterns. (This is before Christina's visualizations). You can see the smaller cistern on the left that branches out from the shaft and the larger cistern is on the right. This map was generated with the sonar data using the sonar mosaics to calculate the ROV position at each of the scans and also SLAM (Simultaneous Localization and Mapping) to help better align the individual scans.

More Projected Geometry

Projected geometry has improved! Surface extraction for a cistern has made it through the pipeline and (as shown below) is now visualized. At the moment, we have a simple keyhole cistern... one of the most common outline shapes for cisterns. It is interesting to see how the sonar scans picked up other objects at the level of the scan that have been interpolated into vertical barriers (seen as pillars).

In addition to surface extraction, I now have multiple projections that can be merged together as a mosaic on the wall of the cistern. Below you can see the mosaic merged together in Microsoft Word on the left. On the right, the same mosaic is replicated in the 3D environment on a wall of the keyhole cistern. The images are actually taken from the ISIS boat trip. On the ISIS, we recorded the ROV's video of the shipwreck. From the video, I took screenshots that represent sequential frames of different features of the shipwreck. With a little patience, I put the images together (as accurately as I could) to represent the shipwreck.

This process will be the same for combining images from the all of the surveyed sites with their corresponding geometry. The mosaic process of projective texturing still has a lot of work to help streamline the process more. Just for the record... this is all REALLY cool :P