Pool Testing at MC LAB

MC-Labben is a basin at Tyholt that we have used for testing during the last years.

Booking and access

The basin has to be booked in advance, usually in the semester before. Evenings and weekends are usually free, so they can often also be booked at shorter notice. For booking we send a mail to one of the following helpful persons

• Emil Bratlie ([email protected])
• Torgeir Wahl ([email protected])

It is usually a good idea to book several days at a time (eg. a weekend), since it takes time to transport all equipment to and from the basin.

For using the basin you also need access to the room. This can be arranged for 5-6 people at a time. Steps for aquiring access:

1. Fill out the formula Avtale for tilgang til adgangskontrollerte områder for each student that wants access. The doors you need are 107, 315 and 316.
2. Get the fomula signed by a teacher/proffessor. We asked Martin Ludvigsen, but Asgeir Sørensen could also be an option.
3. Deliver the formula at the reception at Tyholt in the 3. floor.

Qualisys ground truth camera system

An accurate position of the AUV is needed for proper testing. For this, the Qualisys Track Manager (QTM) software is used in conjunction with six Qualisys 7+ Underwater cameras. An additional three Qualisys 7+ cameras are mounter above water, for full over- and underwater coverage. See their user manual for more info.

Underwater QTM

The PC that is used for QTM underwater is labelled QTM UNDER WATER. Log in with the given credentials. To initialize QTM, follow the Marine cybernetics laboratory handbook Link needed or the QTM user guide.

Calibration

Before the system can be used, it needs to be calibrated. The Qualisys start guide provides a detailed description of how to do this. The TLDR is

1. Acquire the L-shape and the calibration wand.
2. Place the L-shape in the pool to define a reference frame for the calibration process. It is best, though not required, for all six cameras to see the L-shape.
3. Click the "wand" icon in the QTM software GUI (alternatively click CTRL + Shift + ALT + C). Here you can specify calibration settings as you please.
4. After the calibration sequence has started (the blue lights will flash on start and stop), move the wand around the area that is to be used for testing.
5. Once the calibration sequence is finished, the QTM software will tell you if it was successful or not. A successful calibration should be valid for a full day of testing.

NOTE: If you are seeing large, intense markers, it may actually be the other cameras. To filter these out, define the marker size range in Advanced > Marker limits > Default settings: no > Marker size. The range [256, 4096] seems to work fine.

Positioning

To position your object in the water, four reflectors in different heights must be placed on your object. The smaller reflectors have proven to give better results for underwater positioning, as they require lower exposure time. This is especially important when using an object that has reflective parts, such as aluminium surfaces!!

Exposure time should be set to 200 microseconds, and Marker% at 60.

• If you struggle to find the markers, lower the Marker% or increase the exposure.
• If you are letting in too much light to the sensors, lower the exposure.
• If you are capturing too much external noise, increase the Marker% or lower the exposure.

Troubleshooting

Error(s) when waiting for realtime frame.

Try resetting the camera system with the switch located at the other end of the pool (as seen from the command center).

Failed: Too little data

1. Set the calibration time higher, and move the wand around slower.
2. Make sure to rotate and move the wand in all axis.

Failed: Couldn't initialize calibration after reference markers was found.

1. Make sure that both reflectors on the calibration wand is IN VIEW of ALL cameras BEFORE the calibration sequence begins.

Failed: Too few of too many static markers was seen by this camera. The L-frame could not be identified.

1. Check if you have marker masks enabled. If they are, disable them.
2. Make sure that the Exposure & Flash and Marker% are set in a way that captures as little external noise as possible.
3. Turn off all light sources in and around the pool area.
4. Make sure to use the small markers, as the large ones will reflect less than the frame itself..
5. You may also want to define the marker size range in Advanced > Marker limits > Marker size

ROS driver by KTH

The Qualisys motion capture system (QMCS) is available through a network interface on the local network at mc-lab. This local network is available over the bottom switch in the middle of the room, or the mc-lab wifi network. KTH has developed a very nice ros driver that connects to QMCS over this local network. After cloning and build it can be launched with

roslaunch mocap_qualisys comp_qualisys.launch server_address:=192.168.0.20 qtm_protocol_version:=17

where 192.168.0.20 is the IP address of QMCS. The port is 22222 which is default in ros driver. The driver publishes nav_msgs/Odometry on topic.

Problems? Make sure the body name in QMCS does not contain any spaces or weird symbols. Contact Torgeir Wahl if you have problems with the setup.