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Advanced Imaging Magazine

Updated: January 12th, 2011 09:49 AM CDT

Understanding Dynamics of Jettisoned Objects in Wind Currents

falling boxes during a wind-tunnel test
Dual high-speed cameras and frame grabbers captured images of falling boxes during a wind-tunnel test. Three markers on each side of the boxes—with differing weights—provided reference points to help to identify the location and orientation of each box in three dimensions.
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DALSA (St. Laurent, Quebec, Canada)

The Imaging Challenge

The Low-Speed Wind Tunnel in Braunschweig, Germany (NWB), which is operated by German-Dutch Windtunnels (DNW) sought to test the typical trajectories of objects jettisoned from transport aircraft. Wind conditions around the aircraft can cause the boxes to tumble and even move upwards, potentially striking and damaging the aircraft.

Understanding the dynamics of jettisoned objects has applications in fields such as rapid delivery of humanitarian supplies. The DNW-NWB wanted to use the data to validate and refine its airflow simulation software.

The Solution

To perform these tests the DNW-NWB developed the Stereo metric Tracking System to determine the three-dimensional movement of boxes with differing weights falling from the aircraft. Dual high-speed cameras and frame grabbers captured images of the falling boxes, acting as the "eyes" of a vision system that used the two images to reconstruct the 3D co-ordinates of each box. Three markers on each side of the boxes provided reference points to help to identify the location and orientation of each box.

The performance needs of the Stereo metric Tracking System were high. Two Mikrotron MC1310 cameras captured images of 1280x1024 pixels at 500 frames/second. This requires a system capable of handling a data rate of 655 Mpixels/sec from each camera to its corresponding frame grabber. To meet this need, the DNW-NWB selected DALSA's Xcelera frame grabbers, which are capable of handling data rates of up to 1 Gbyte/second both on input and output over its 4-lane PCIe interface.

To process the image data and extract the 3D position, the frame grabbers ran DALSA's Sapera LT image processing software along with user-supplied analysis software. The user software, picColor from FIBUS, handled the 3D position extraction and trajectory tracking. Once the system extracted and stored the tracking data it discarded the images.

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