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.

A Break in the Action

During our trip to the archive in Mdina there was a brief period when our host at the archive had to take a lunch break, so we decided to take the opportunity to walk around the beautiful Silent City and get a quick snack. We cruised into one of the local restaurants for some cake and drinks. Each one of us chose a different cake, trading bites of our slice for others that also looked delicious. I also tried a local soft drink called Kinnie that a few of us decided tastes like a cross between ginger ale and root beer.

Afterwards, we headed to the Eastern wall of Mdina to overlook the far side of the island. Mdina is on the West side of Malta, but seeing to the Eastern coast was no trouble from our vantage point. We also took the opportunity to snap a group photo before heading back to finish up with the archive.

Mdina, Round 1

Our site for Wednesday was within the walled city of Mdina (http://en.wikipedia.org/wiki/Mdina). The first cistern was located in a restaurant called Bacchus, which was not open for the day yet.

This caused our time for exploration to be slightly shortened, as we had to be out before they opened. After arriving, during setup and some of the time spent in the cistern, about half of the team was able to wander around the restaurant with the owner getting a bit of a history lesson. There was much history to discuss since the room was built between 1657 and 1660! Since it was before business hours, many people transporting supplies for Bacchus were filtering in and out of the front entrance where we were located. Many stopped momentarily to see what we were doing, and were very interested in our sonar maps of the underside of the restaurant as well as the images we were receiving from the VideoRay.

In an effort to rotate drivers during different sites, Christina watched closely as I drove the VideoRay through this site so she could become familiar with the logging process and hopefully gather useful data. After gathering data for awhile, the ToughBook lost communication with the control box. After a quick bit of unsuccessful troubleshooting, it was about time to leave, so we headed to the next location.

The next spot was The Mdina Experience, right down the street. There was very limited space here, and it was during normal business hours.

There was actually a tour group passing right through our site when we arrived. They watched as we brought in and setup all of our equipment, but weren't interested enough to ask any questions. We switched to the Samsung backup since we thought the problem was with the ToughBook and did not have time to continue troubleshooting it on-site. Slightly different connections had to be made when using the Samsung, since it lacked a serial port, but everything worked out and we got the VideoRay through the small entrance and into the water.

Space was limited, so team members not directly involved couldn't really be present, so exploration presented itself again!

Another restaurant was our final location of the day. The cistern here was located in the basement. We had to walk through the restaurant which caused for some further stares of the other patrons. There was an extremely narrow passageway leading down to the site, and our equipment had to make it carefully down the long staircase. To add a bit to difficulty, the passageway was lined with wine bottles so there was little room for error. Luckily, Tyler and I made it all the way down successfully.

After making it downstairs and setting up, the data collection process began. Christina drove for for the first time on this site, and did an awesome job grabbing sonar scans and video for the cistern we were on top of. This cistern was composed of a large circular room and a narrow hallway that didn't lead to anything. We ended our day here, and loved the view off the balcony behind the restaurant!

A Rocky Beginning

We've had an exciting last few days exploring our sites, but we've been having some technical issues along the way. First, upon opening one of the control boxes we discovered that one of the LCD screens was badly damaged. Attempts to use it were unfruitful. Fortunately, the other display is still intact, and it does not seem like we'll be needing either soon.

At our first location, Gomerino Palace, we had some good data collection which was accompanied by some minor mishaps. When trying to use a power strip with US sockets and a socket adapter during our a we quickly realized that a US power strip meant for 120 volt sockets will not handle 240 volt sockets. The second could not be explored since the water level was not high enough. Our third cistern happened to be surrounded by a lot plants, so there were a lot of roots hanging down into the cistern. After a few minutes of driving the ROV around many small roots got stuck in the top propeller. Someone noticed quickly and we were able to get the ROV out and clear the roots off and continue.

The second area we visited was the city of Mdina, former capital of Malta known as the Silent City. Our first site was the Bacchus restaurant which was built in the walls of the city. Data collection went relatively smoothly at this location, with the exception that this was the beginning of a recurring problem with the depth sensor not reading correctly. We also were not able to get HD footage since the battery in our camera died after about 3 minutes. There was a minor hiccup with the USB ports on our toughbook, but restarting seemed to remedy that for the time being. This didn't affect our sonar measurements since it was connected through the serial ports rather than USB. The USB issues continued at our next two sites, the Mdina Experience and a third restaurant, so we used one of our Samsung laptops instead of the toughbook. There were a few communication issues between our laptop and the ROV, but restarting both the laptop and the control box for the ROV resolved these problems.

Before our second trip to Mdina we decided to recalibrate our depth sensors at a local gas station, which seemed to work at the time, but did not once we got on site at the St. Paul's Cathedral Museum, so we switched to static mapping. This is just a fancy way of saying that our robot is sitting still while taking sonar measurements. Using this technique we get 2D maps instead of 3D maps since we do not move up and down to get sonar readings at different depths. Our HD camera was fully charged this time and got some good video. Other than the depth sensor, the only major issue we had at the Cathedral and the Cathedral Museum was the fact that some of the waterways were more shallow than we had hoped for, so we weren't able to explore as easily into some areas as we had hoped for. We did get some interesting readings as we thought two of the waterways we were looking at would be connected directly, but actually had tunnels that went in different directions. Overall, we've had a rocky start, both trying to recover from jet lag and making sure our robot is working well enough to get data, but we still have a lot to show for it.