Steerable Gaussian derivative filter. This function is meant for visualization only. It is a demonstration of steerable filters. Analytically find Gx = dxG and Gy = dxG. Then find the derivative of G in some arbitrary direction theta by taking a linear combination of Gx and Gy. INPUTS theta - orientation EXAMPLE filter_steerable( 30 ) DATESTAMP 29-Sep-2005 2:00pm