% GetSegyHeader : Reads the segyheader of a SEGY Y formatted file

%

% Call :

%  [SegyHeader]=GetSegyHeader(segyid);

%

%  segyid can be a filehandle or a filename

%  



%

% (C) 2001-2004 Thomas Mejer Hansen, tmh@gfy.ku.dk/thomas@cultpenguin.com

%

%

%    This program is free software; you can redistribute it and/or modify

%    it under the terms of the GNU General Public License as published by

%    the Free Software Foundation; either version 2 of the License, or

%    (at your option) any later version.

%

%    This program is distributed in the hope that it will be useful,

%    but WITHOUT ANY WARRANTY; without even the implied warranty of

%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

%    GNU General Public License for more details.

%

%    You should have received a copy of the GNU General Public License

%    along with this program; if not, write to the Free Software

%    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

%

function [SegyHeader]=GetSegyHeader(segyid,varargin);



  mfilename='GetSegyHeader';



  SegymatVerbose([mfilename,' : Start'],90);



  ninput=nargin;

  % NEXT TWO LINES TO ENUSRE THAT VARARGIN CAN BE PASSED TO FUNCTION

  if ninput==2

    % CALL USING VARARGIN

    ninput=1+length(varargin{1});

    varargin=varargin{1};

  else

    % DIRECT CALL

    ninput=length(varargin);

  end

  

  

  % TRANSFORM VARARGING INTO PARAMETERS

  cargin=1;

  while (cargin<ninput)

       

    % ENDIAN FORMAT 

    endian='ieee-be'; % Big Endian is default

    if strcmp(varargin{cargin},'endian')

      cargin=cargin+1;

      eval(['endian_tight=varargin{cargin};'])

      if endian_tight=='l',

        SegymatVerbose(['USING LITTLE ENDIAN TYPE'])

        endian='ieee-le';

      else

        SegymatVerbose(['USING BIG ENDIAN TYPE'])

      end

    end    

    

    if strcmp(varargin{cargin},'revision')

      cargin=cargin+1;

      eval(['revision=',num2str(varargin{cargin}),';']);

      SegymatVerbose(['USING REVISION : rev=',num2str(revision)])

    end    

    

    if strcmp(varargin{cargin},'dsf')

      cargin=cargin+1;

      eval(['dsf=',num2str(varargin{cargin}),';']);

      SegymatVerbose(['USING Data Sample Format : dsf=',num2str(dsf)])

    end    

    

    if strcmp(varargin{cargin},'SkipData')

      cargin=cargin+1;

      eval(['SkipData=',num2str(varargin{cargin}),';']);

      SegymatVerbose(['SKIPPING DATA - READING ONLY HEADERS'])

    end    

    

   

      cargin=cargin+1;

      

  end

  

  

  

if isstr(segyid)

    % if segyid is a string it is interpreted as a filename

    %

    segyid = fopen(segyid,'r','b');   % ALL DISK FILES ARE IN BIG

                                    % ENDIAN FORMAT, ACCORDING TO SEG

                                    % Y rev 1

    whos

end



% Basic Segy Header Information.

SegyHeader.Rev=GetSegyHeaderBasics;



fseek(segyid,0,'bof');

SegyHeader.TextualFileHeader=fread(segyid,3200,'uchar');         % 3200

SegyHeader.Job=fread(segyid,1,'int32');                           % 3204 

SegyHeader.Line=fread(segyid,1,'int32');                          % 3208

SegyHeader.Reel=fread(segyid,1,'int32');                          % 3212

SegyHeader.DataTracePerEnsemble=fread(segyid,1,'int16');        % 3214

SegyHeader.AuxiliaryTracePerEnsemble=fread(segyid,1,'int16');   % 3216

SegyHeader.dt=fread(segyid,1,'uint16');                          % 3218

SegyHeader.dtOrig=fread(segyid,1,'uint16');                      % 3220

SegyHeader.ns=fread(segyid,1,'uint16');                          % 3222

SegyHeader.nsOrig=fread(segyid,1,'uint16');                      % 3224

SegyHeader.DataSampleFormat=fread(segyid,1,'int16');            % 3226

SegyHeader.EnsembleFold=fread(segyid,1,'int16');                

SegyHeader.TraceSorting=fread(segyid,1,'int16');               % 3228

SegyHeader.VerticalSumCode=fread(segyid,1,'int16');            % 3230



SegyHeader.SweepFrequencyStart=fread(segyid,1,'int16');        % 3232

SegyHeader.SweepFrequencyEnd=fread(segyid,1,'int16');          % 3234

SegyHeader.SweepLength=fread(segyid,1,'int16');                % 3236

SegyHeader.SweepType=fread(segyid,1,'int16');                  % 3238

SegyHeader.SweepChannel=fread(segyid,1,'int16');               % 3240

SegyHeader.SweepTaperlengthStart=fread(segyid,1,'int16');               % 3242

SegyHeader.SweepTaperLengthEnd=fread(segyid,1,'int16');               % 3244

SegyHeader.TaperType=fread(segyid,1,'int16');               % 3246



SegyHeader.CorrelatedDataTraces=fread(segyid,1,'int16');               % 3248



SegyHeader.BinaryGain=fread(segyid,1,'int16');               % 3250

SegyHeader.AmplitudeRecoveryMethod=fread(segyid,1,'int16');               % 3252



SegyHeader.MeasurementSystem=fread(segyid,1,'int16');               % 3254



SegyHeader.ImpulseSignalPolarity=fread(segyid,1,'int16');               % 3256

SegyHeader.VibratoryPolarityCode=fread(segyid,1,'int16');               % 3258



% 3261-3500 UNASSIGNED (as 120*2byte integer)

SegyHeader.Unassigned1=fread(segyid,120,'int16');               % 3260



% fseek(segyid,3500,'bof');

SegyHeader.SegyFormatRevisionNumber=fread(segyid,1,'uint16');   % 3500

SegyHeader.FixedLengthTraceFlag=fread(segyid,1,'integer*2');        % 3502

SegyHeader.NumberOfExtTextualHeaders=fread(segyid,1,'uint16');        % 3504



% 3506-3600 UNASSIGNED (as 47*2byte integer = 94 byte)

SegyHeader.Unassigned2=fread(segyid,47,'int16');               % 3506



% READ TEXTURAL FILE HEADER EXTENSION IF NEEDED

%fseek(segyid,3600,'bof');

if (SegyHeader.NumberOfExtTextualHeaders>0),

  SegymatVerbose(['---------------------------------------------------'])

  SegymatVerbose(['extended textual file headers are implemented      '])

  SegymatVerbose(['but have not been tested, since I(tmh@gfy.ku.dk)   '])

  SegymatVerbose(['have had no access to SEGY REV-1 files formatted   '])

  SegymatVerbose(['like this. Please contact me if you have such a    '])

  SegymatVerbose(['file to share   '])

  SegymatVerbose(['---------------------------------------------------'])



  

  txt=sprintf('%d Extended Textual File Headers',SegyHeader.NumberOfExtTextualHeaders);

  SegymatVerbose(txt);

  nChars=3200*SegyHeader.NumberOfExtTextualHeaders;

  SegyHeader.ExtTextualHeaders=fread(segyid,nChars,'schar');        % 3600

else

  SegymatVerbose('NO extended textual file headers');

end







SegyHeader.time=[1:1:SegyHeader.ns].*SegyHeader.dt./1e+6;



Revision=SegyHeader.SegyFormatRevisionNumber;

if Revision>0, Revision=1; end



if (SegyHeader.DataSampleFormat>length(SegyHeader.Rev(Revision+1).DataSampleFormat));

SegymatVerbose([mfilename,' : WARNING : YOU HAVE SELECTED (OR THE FILE IS FORMATTED SUCH THAT) A DATASAMPLE FORMAT THAT IS NOT DEFINED. \nREMEBER IEEE IS NOT SPECIFIED IN THE SEGY REV0 STANDARD !'])

     

  if (Revision==0)

    SegymatVerbose([mfilename,' : TRYING TO USE REVISION 1 AS OPPOSED TO REVISION 0'])

    Revision=1;

     

    if (SegyHeader.DataSampleFormat>length(SegyHeader.Rev(Revision+1).DataSampleFormat));

      SegymatVerbose([mfilename,' : FATAL ERROR : STILL THE DATASAMPLE FORMAT IS NOT SUPPRTED - EXITING (Report error to tmh@gfy.ku.dk)'])

    else 

      SegymatVerbose([mfilename,' : APPARENT SUCCES CHANING FROM Revision 0 to 1 - Continuing'])

      SegyHeader.SegyFormatRevisionNumber=1; % FORCING REVISION TO BE 1 !!!

    end

     

   end

     

end



try

  Format=SegyHeader.Rev(Revision+1).DataSampleFormat(SegyHeader.DataSampleFormat).name;

  SegymatVerbose([mfilename,' : SegyRevision ',sprintf('%0.4g',Revision),', ',Format,'(',num2str(SegyHeader.DataSampleFormat),')'])

catch

end

  

if isstr(segyid)

    fclose(segyid);

end



  SegymatVerbose([mfilename,' : End'],90);