Obtaining whisker position from line camera data.

<p><b>A)</b> A single scan from one line camera (top). The spatial irregularities of the raw scan are due primarily to non-uniform illumination from the diodes. These irregularities are removed by subtracting a baseline scan (green), which is obtained with no whisker present. After subtracting the baseline scan, the whisker shadow waveform is clearly visible (middle). Finally, the scan is low-pass filtered so that the minimum point precisely identifies the pixel at the center of the whisker shadow (bottom). <b>B)</b> The pixel positions of the shadows (<i>p_x</i> and <i>p_y</i>) are then used to compute the actual spatial positions (x and y): <i>x</i> = (<i>d_c</i> - <i>p_y d_c</i>/<i>d_s</i>)/(<i>d_s</i>/<i>p_x</i>+<i>p_y</i>/<i>d_s</i>) and <i>y</i> = <i>p_y</i> (<i>d_c</i>+<i>x</i>)/<i>d_s</i>. These formulas are geometrically derived from the diagram shown here.