def _distance(image, bands): return evaluate_pairwise(image, bands, 'hypot(b1, b2)', 'distance_${b1}_${b2}')
def _angle(image, bands): return evaluate_pairwise(image, bands, 'atan2(b1, b2) / pi', 'angle_${b1}_${b2}')
def _ratio(image, bands): return evaluate_pairwise(image, bands, 'b1 / b2', 'ratio_${b1}_${b2}')
def _diff(image, bands): return evaluate_pairwise(image, bands, 'b1 - b2', 'diff_${b1}_${b2}')
def _normalized_difference(image, bands): return evaluate_pairwise(image, bands, '(b1 - b2) / (b1 + b2)', 'nd_${b1}_${b2}')