function nav = readnav(filename)

nav.latitude = NaN;
nav.longitude = NaN;
nav.time = NaN;

n = 0;
i = 0;
fid = fopen(filename);
while ~feof(fid)
    n = n + 1;
    line = fgetl(fid);
    if n > 10
        i = i + 1;
        nav.latitude(i) = str2double(stringtokenizer(line, 2, sprintf('\t')));
        nav.longitude(i) = str2double(stringtokenizer(line, 3, sprintf('\t')));
        nav.time(i) = datenum(stringtokenizer(line, 1 , sprintf('\t')), 'yyyy/mm/dd hh:MM:ss PM');
    end
end
fclose(fid);
[nav.time, idx] = sort(nav.time);
nav.longitude = nav.longitude(idx);
nav.latitude = nav.latitude(idx);