Calibration Work in the Ultrasound Project

Ultrasound calibration involves tracking the ultrasound probe, and determining a transformation from the ultrasound 2D image space to the probe's local coordinate system. Then when the tracking system tells us where the probe is in world space, we can determine the location in world space of each pixel in the ultrasound image.

Video calibration involves tracking the see-through head-mounted display, and determining a transformation from image space of the video camera atop the HMD to the HMD's local coordinate system. Thus if we put an object in the virtual world that matches something in the real world, they will appear to coincide to the HMD wearer. This calibration involves measuring the camera's position, orientation, and optical characteristics (field of view, radial distortion coefficients, and the center of distortion in screen space).

This picture shows the view through the video camera of the calibration rig, designed and built by Andrei State. Note how the computer draws zig-zag lines coorespond to the grid on the real world box.

This picture shows our ultrasound experment performed with a baby doll suspended in an acquarium. Note how the computer drawn lines bend to match the acquarium, and the computer drawn doll matches the real doll. They both demonstrate the quality of our video calibration. The doll also demonstrates the quality of our ultrasound calibration, since ~80 arbitrarily positioned ultrasound images are combined to make a volume data set.