function read_ltsahead
%
% read LTSA header and directories 
%
% 060612 smw ver 1.61
%
% tic

global PARAMS HANDLES

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% open input ltsa file
fid = fopen([PARAMS.ltsa.inpath,PARAMS.ltsa.infile],'r');

%%%%%%%%%%%%%%%%%%%%%%%%%
%
% LTSA Header - 64 bytes
%
type = fread(fid,4,'char');                    % 4 bytes - file ID type
ver = fread(fid,1,'uint8');                    % 1 byte - version number
spare = fread(fid,3,'char');                   % 3 bytes - spare
PARAMS.ltsa.dirStartLoc = fread(fid,1,'uint32');           % 4 bytes - directory start location [bytes]
PARAMS.ltsa.dataStartLoc = fread(fid,1,'uint32');          % 4 bytes - data start location [bytes]
PARAMS.ltsa.tave = fread(fid,1,'float32');     % 4 bytes - time bin average for spectra [seconds]
PARAMS.ltsa.dfreq = fread(fid,1,'float32');    % 4 bytes - frequency bin size [Hz]
PARAMS.ltsa.fs = fread(fid,1,'uint32');        % 4 bytes - sample rate [Hz]
PARAMS.ltsa.nfft = fread(fid,1,'uint32');      % 4 bytes - number of samples per fft
PARAMS.ltsa.nrftot = fread(fid,1,'uint16');    % 2 bytes - total number of raw files from all xwavs
PARAMS.ltsa.nxwav = fread(fid,1,'uint16');     % 2 bytes - total number of xwavs files used
% 36 bytes used, up to here
% pad header for future growth, but backward compatible
fseek(fid,28,0);                  % 1 bytes x 28 = 28 bytes - 0 padding / spare
% 64 bytes used - up to here
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% directory
%
% define/initialize some vectors first instead of dynamically - this should
% be faster

PARAMS.ltsahd.year = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsahd.month = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsahd.day = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsahd.hour = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsahd.minute = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsahd.secs = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsahd.ticks = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsa.byteloc = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsa.nave = zeros(1,PARAMS.ltsa.nrftot);

PARAMS.ltsahd.fname = zeros(PARAMS.ltsa.nrftot,40);

PARAMS.ltsahd.rfileid = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsa.dnumStart = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsa.dvecStart = zeros(PARAMS.ltsa.nrftot,6);
PARAMS.ltsa.dnumEnd = zeros(1,PARAMS.ltsa.nrftot);
PARAMS.ltsa.dvecEnd = zeros(PARAMS.ltsa.nrftot,6);


for k = 1 : PARAMS.ltsa.nrftot
    % write time values to directory
    PARAMS.ltsahd.year(k) = fread(fid,1,'uchar');          % 1 byte - Year
    PARAMS.ltsahd.month(k) = fread(fid,1,'uchar');         % 1 byte - Month
    PARAMS.ltsahd.day(k) = fread(fid,1,'uchar');           % 1 byte - Day
    PARAMS.ltsahd.hour(k) = fread(fid,1,'uchar');          % 1 byte - Hour
    PARAMS.ltsahd.minute(k) = fread(fid,1,'uchar');        % 1 byte - Minute
    PARAMS.ltsahd.secs(k) = fread(fid,1,'uchar');          % 1 byte - Seconds
    PARAMS.ltsahd.ticks(k) = fread(fid,1,'uint16');        % 2 byte - Milliseconds
    % 8 bytes up to here
    %
    PARAMS.ltsa.byteloc(k) = fread(fid,1,'uint32');     % 4 byte - Byte location in ltsa file of the spectral averages for this rawfile
    PARAMS.ltsa.nave(k) = fread(fid,1,'uint16');          % 2 byte - number of spectral averages for this raw file
    % 14 bytes up to here
    PARAMS.ltsahd.fname(k,:) = fread(fid,40,'uchar');        % 40 byte - xwav file name for this raw file header
    PARAMS.ltsahd.rfileid(k) = fread(fid,1,'uint8');       % 1 byte - raw file id / number for this xwav
    % 55 bytes up to here
    fseek(fid,9,0);                    % 9 bytes zero padding / spare
    % 64 bytes for each directory listing for each raw file
    
    % stolen from rdxwavhd.m:
    % calculate starting time [dnum => datenum in days] for each ltsa raw
    % file ie write/buffer flush
    PARAMS.ltsa.dnumStart(k) = datenum([PARAMS.ltsahd.year(k) PARAMS.ltsahd.month(k)...
        PARAMS.ltsahd.day(k) PARAMS.ltsahd.hour(k) PARAMS.ltsahd.minute(k) ...
        PARAMS.ltsahd.secs(k)+(PARAMS.ltsahd.ticks(k)/1000)]);
    PARAMS.ltsa.dvecStart(k,:) = [PARAMS.ltsahd.year(k) PARAMS.ltsahd.month(k)...
        PARAMS.ltsahd.day(k) PARAMS.ltsahd.hour(k) PARAMS.ltsahd.minute(k) ...
        PARAMS.ltsahd.secs(k)+(PARAMS.ltsahd.ticks(k)/1000)];
    
            PARAMS.ltsa.dur(k) = PARAMS.ltsa.tave * PARAMS.ltsa.nave(k);
            
    % end of ltsa for each raw file:
    PARAMS.ltsa.dnumEnd(k) = PARAMS.ltsa.dnumStart(k) ...
        + datenum([0 0 0 0 0 (PARAMS.ltsa.dur(k) - 1/PARAMS.ltsa.fs)]);
    PARAMS.ltsa.dvecEnd(k,:) = PARAMS.ltsa.dvecStart(k,:) ...
        + [0 0 0 0 0 (PARAMS.ltsa.dur(k) - 1/PARAMS.ltsa.fs)];
    
end

PARAMS.ltsa.durtot = sum(PARAMS.ltsa.dur);

% close file
fclose(fid);

% number of frequencies in each spectral average:
PARAMS.ltsa.nf = PARAMS.ltsa.nfft/2 + 1;	

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% initialize the timing parameters
PARAMS.ltsa.start.dnum = PARAMS.ltsa.dnumStart(1);
PARAMS.ltsa.start.dvec = PARAMS.ltsa.dvecStart(1,:);
PARAMS.ltsa.end.dnum = PARAMS.ltsa.dnumEnd(PARAMS.ltsa.nrftot);

% max freq
PARAMS.ltsa.fmax = PARAMS.ltsa.fs/2;

% frequency bin indices
PARAMS.ltsa.fimin = 1;
PARAMS.ltsa.fimax = PARAMS.ltsa.nf;

% frequency bins
PARAMS.ltsa.freq = [0:PARAMS.ltsa.dfreq:PARAMS.ltsa.fmax];
PARAMS.ltsa.f = PARAMS.ltsa.freq;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

set(HANDLES.ltsa.endfreq.edtxt,'String',num2str(PARAMS.ltsa.fmax))

% turn on mouse coordinate display
set(HANDLES.fig.main,'WindowButtonMotionFcn','control(''coorddisp'')');
set(HANDLES.fig.main,'WindowButtonDownFcn','pickxyz');

% turn on msg window edit text box for pickxyz display
set(HANDLES.pick.disp,'Visible','on')
% turn on pickxyz toggle button
set(HANDLES.pick.button,'Visible','on')
% enable msg window File pulldown save pickxyz
set(HANDLES.savepicks,'Enable','on')

% t=toc;
% disp_msg(['Time to read ltsahead = ',num2str(t)])