function f = loc_feat(model, num_levels)
% Location and scale features.
%   f = loc_feat(model, num_levels)
%
%   Compute a feature indicating if level i is in the first octave of 
%   the feature pyramid, the second octave, or above. This could be
%   generalized to a "location feature" instead of just a scale feature.
%
% Return value
%   f = [f_1, ..., f_i, ..., f_num_levels],
%   where f_i is the 3x1 vector = 
%     [1; 0; 0] if 1 <= i <= model.interval
%     [0; 1; 0] if model.interval+1 <= i <= 2*model.interval
%     [0; 0; 1] if 2*model.interval+1 <= i <= num_levels
%
% Arguments
%   model       Model used for detection
%   num_levels  Number of levels in the feature pyramid

f = zeros(3, num_levels);

b = 1;
e = min(num_levels, model.interval);
f(1, b:e) = 1;

b = e+1;
e = min(num_levels, 2*e);
f(2, b:e) = 1;

b = e+1;
f(3, b:end) = 1;