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ReadSegyHeader.m
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ReadSegyHeader.m
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% ReadSegyHeader : Reads a SEG Y Binary Header
%
% Call :
% [SegyHeader]=ReadSegyHeader(filename);
%
% To read using little endian :
% [SegyHeader]=ReadSegyHeader(filename,'endian','l');
%
% (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]=ReadSegyHeader(filename,varargin);
if ~(exist(filename)==2'),
SegymatVerbose([mfilename,' : ', filename,' does not exist !'])
Data=[];SegyTraceHeaders=[];SegyHeader=[];HeaderInfo=[];
return
end
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)
if strcmp(varargin{cargin},'jump')
cargin=cargin+1;
eval(['jump=',num2str(varargin{cargin}),';']);
SegymatVerbose(['JUMP : Read only every ',num2str(jump),'th trace'])
end
if strcmp(varargin{cargin},'minmax')
cargin=cargin+1;
eval(['header=''',varargin{cargin},''';']);
cargin=cargin+1;
eval(['headermin=',num2str(varargin{cargin}),';']);
cargin=cargin+1;
eval(['headermax=',num2str(varargin{cargin}),';']);
SegymatVerbose(['MIN MAX : Using header ',header,' from ',num2str(headermin),' to ',num2str(headermax)])
end
if strcmp(varargin{cargin},'trange')
cargin=cargin+1;
eval(['tmin=',num2str(varargin{cargin}),';']);
cargin=cargin+1;
eval(['tmax=',num2str(varargin{cargin}),';']);
SegymatVerbose(['TRANGE : tmin=',num2str(tmin),' tmax=',num2str(tmax)])
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},'SegyHeader')
cargin=cargin+1;
SegyHeader=varargin{cargin};
SegymatVerbose(['USING LOADED SEGYHEADER'])
end
% 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
cargin=cargin+1;
end
if exist('SkipData','var')==0,
SkipData=0; % [0] READ ONLY HEADER VALUES, [1] READ IN ALL DATA
end
if SkipData==1, SegymatVerbose(['Not reading data - headers only']), end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% TRY TO ESTIMATE NUMBER OF TRACES
if exist('endian')==1,
segyid = fopen(filename,'r',endian);
else
segyid = fopen(filename,'r','ieee-be'); % ALL DISK FILES ARE IN BIG
end % ENDIAN FORMAT, ACCORDING TO
% SEGY Y rev 1
SegyHeader=GetSegyHeader(segyid);
try
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
FormatName=SegyHeader.Rev(Revision+1).DataSampleFormat(SegyHeader.DataSampleFormat).name;
Format=SegyHeader.Rev(Revision+1).DataSampleFormat(SegyHeader.DataSampleFormat).format;
BPS=SegyHeader.Rev(Revision+1).DataSampleFormat(SegyHeader.DataSampleFormat).bps;
txt=['SegyRevision ',sprintf('%0.4g',Revision),', ',FormatName,'(',num2str(SegyHeader.DataSampleFormat),')'];
fseek(segyid,0,'eof'); DataEnd=ftell(segyid);
DataStart=3600+3200*SegyHeader.NumberOfExtTextualHeaders;
fseek(segyid,DataStart,'bof'); % Go to the beginning of the file
fseek(segyid,DataStart,'bof'); % Go to the beginning of the file
SegyHeader.ntraces=(DataEnd-DataStart)./(240+(SegyHeader.ns)*(BPS/8));
catch
% could not estimate ntraces
end
fclose(segyid);