s_select.m

地震、测井方面matlab代码,解释的比较详细

function seisout=s_select(seismic,varargin)
% Function extracts subset of seismic input traces. An option also allows changing the time
% range of the output data. If seisout.first < seismic.first and/or seisout.last > seismic.last
% then the trace samples undefined by the input data are set to the null value.
% Written by E. R., April 15, 2000
% Last updated: September 24, 2004: allow use of PARAMETERS4FUNCTION
% See also: s_append
%
%          seisout=s_select(seismic,varargin)
% INPUT
% seismic  seismic structure
% varargin one or more cell arrays; the first element of each cell array is a keyword string,
%          the following arguments contains a parameter(s). 
%          Accepted keywords are:
%          times  For a two-element cell array the second element is a vector of time values.
%                 For a three-element cell array the second and third element contain the 
%                 time of the first sample and the last sample respectively.
%                 Default: {'times',[]}
%                 which is equivalent to {'times',seismic.first,seismic.last}
%          traces The second element can be a vector of trace numbers or it can be a string.
%                 If it is a string it can be a header mnemonic or it can contain a logical 
%                 expression involving header values to include.
%                 A "pseudo-header" 'trace_no' can also be used.
%                 If the second element is a string containing a header mnemonic there must 
%                 be a third element containing a vector of values
%                 Default:  {'traces',[]} which is equivalent to 
%                           {'traces',1:ntr} where ntr denotes the number of traces in the 
%                              input data set (ntr = size(seismic.traces,2))
%                 Headers are selected as found and are not sorted.
%          null   Null value to assign to seismic data values for times < seismic.first or
%                 > seismic.last. 
%          Default: "null=0" unless seismic has null values; then "null=NaN".
%             
%       Examples: s_select(seismic,{'traces',1:10})             % Select traces 1 to 10
%                 s_select(seismic,{'traces','trace_no',1:10})  % Same as above
%                 s_select(seismic,{'traces','trace_no',1,10})  % Same as above
%                 s_select(seismic,{'times',0,1000},{'traces','cdp',100:10:200}) %
%                          % Select traces with CDP numbers 100 t0 200 with increment 10
%                 s_select(seismic,{'times',seismic.first:2*seismic.step:seismic.last})
%
%                 s_select(seismic,{'traces','cdp',100,inf})  % Select traces with CDP's 100 and above
%                 s_select(seismic,{'traces','cdp >= 100'})   % This is equivalent to the previous command
%                 s_select(seismic,{'traces','iline_no > 1000 & iline_no < 1100 & xline_no == 1000'})
%                                             
% OUTPUT
% seisout  seismic output structure

global S4M

if ~isstruct(seismic)
   error('"seismic" must be a structure')
end
if ~strcmp(seismic.type,'seismic')
   error('Input is not a seismic dataset')
end

seisout=seismic;

[nsamp,ntr]=size(seismic.traces);

%       Set defaults for input parameters
param.times=[];
param.traces=[];
if isfield(seismic,'null')
   param.null=seismic.null;
else
   param.null=0;
end

%       Decode and assign input arguments
param=assign_input(param,varargin,'s_select');

if isempty(param.times)
   param.times={seismic.first,seismic.last};
end

%      Determine index for times
if iscell(param.times)
   ta=param.times{1};
   te=param.times{2};
   if te < ta
      error(['First time (',num2str(ta),' greater than last time (',num2str(te),')'])
   end
   nta=round((ta-seismic.first)/seismic.step);
   ta=nta*seismic.step+seismic.first;
   nte=round((te-seismic.first)/seismic.step);
   te=nte*seismic.step+seismic.first;
   t_index=nta+1:nte+1;
   seisout.step=seismic.step;

else
   t_index=round((param.times-seismic.first)/seismic.step)+1;
   ta=(min(t_index)-1)*seismic.step+seismic.first;
   te=(max(t_index)-1)*seismic.step+seismic.first;
   if length(t_index) > 1
      dt=diff(t_index);
      if max(dt) ~= min(dt)
         error('Nonuniform time samples selected')
      else
         seisout.step=dt(1)*seismic.step;
      end
   else
      seisout.step=seismic.step;
   end
end
seisout.first=ta;
seisout.last=te;

%       Find index for traces
if isempty(param.traces)
   h_index=1:ntr;

else
  if ~iscell(param.traces)
    param.traces={param.traces};
  end
  if ~ischar(param.traces{1})            % Traces given explicitely
    if length(param.traces) > 1
      h_index=max([1,param.traces{1}]):min([size(seismic.traces,2),param.traces{2}]);
    else
      h_index=param.traces{1};
    end
    if max(h_index) > ntr
      error([' Only ',num2str(ntr),' trace(s) available, but largest trace number selected: ',num2str(max(h_index))])
    end

  elseif length(param.traces) > 1        % Traces defined via header
    header=lower(param.traces{1});
    if isfield(seismic,'header_info')
      idx=ismember_ordered(lower(seismic.header_info(:,1)),header);
    else
      idx=[];
    end
    if isempty(idx)
      if strcmp(header,'trace_no')
        header_vals=1:ntr;
      else
        error(['Header "',header,'" not present in seismic input structure'])
      end
    else
      header_vals=seismic.headers(idx,:);
    end

    if length(param.traces) == 2   % Range of header values specified
      hidx=param.traces{2};
      h_index=ismember_ordered(header_vals,hidx);
      if isempty(h_index)
        error(['Header "',header,'" has no values matching the ones requested'])
      end

    else                        % First and last header value specified
      ha=param.traces{2}; 
      he=param.traces{3};
      h_index=find(header_vals >= ha & header_vals <= he);
      if isempty(h_index)
        error(['Header "',header,'" has no values within range specified (',num2str([ha,he]),')'])
      end
    end

  else                                    % Traces defined via logical expression
     h_index=find_trace_index(seismic,param.traces{1});
  end
end

%     Copy seismic data
if ta < seismic.first | te > seismic.last
  if param.null == 0
    seisout.traces=zeros(length(t_index),length(h_index));
  else
    seisout.null=param.null;
    seisout.traces=param.null*ones(length(t_index),length(h_index));
  end
  idxi=find(ismember(1:nsamp,t_index));
  idxo=find(ismember(t_index,1:nsamp));
  if isempty(idxi)
    error([' Time range specified (',num2str(ta),' - ',num2str(te), ...
          ') does not include time range of input data (', ...
          num2str(seismic.first),' - ',num2str(seismic.last),')'])
  end
  seisout.traces(idxo,:,:)=seismic.traces(idxi,h_index,:);
else
  seisout.traces=seismic.traces(t_index,h_index,:);
end

%     Copy headers
if isfield(seismic,'headers')
   seisout.headers=seismic.headers(:,h_index);
end

% 	Check for existence of null values
if S4M.matlab_version >= 7.0
   bool=~isempty(find(isnan(seisout.traces),1));
else
   bool=~isempty(find(isnan(seisout.traces)));
end

if bool
   seisout.null=NaN;
else
   if isfield(seisout,'null')
      seisout=rmfield(seisout,'null');
   end
end


%    Append history field
if S4M.history & isfield(seismic,'history')
   htext=['Times: ',num2str(seisout.first),' - ',num2str(seisout.last),' ',seisout.units,', ', ...
          num2str(length(h_index)),' traces'];
   seisout=s_history(seisout,'append',htext);
end

if isempty(seisout.traces)
   display(' Alert from "s_select": No traces selected. Empty trace matrix output')
end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function index=find_trace_index(seismic,expression)
% Function finds index of traces whose header values match a logical expression
% INPUT
% seismic       seismic data set
% expression    logical expression involving header values
% OUTPUT
% index         index of trace numbers (traces "seismic.traces(:,h_index)" are selected)

words=symvar(expression);

ik=0;
for ii=1:length(words)
   temp=find(ismember(seismic.header_info(:,1),words(ii)));    
   if isempty(temp)
      ik=ik+1;
      if strcmp(words(ik),'trace_no')   % Trace_no is used in expression "expression"
         trace_no=1:size(seismic.headers,2); 
      end
   else
      ik=ik+1;
      eval([words{ik},'=seismic.headers(temp,:);']);
   end
end
if ik == 0
   disp([' No header mnemonics in expression "',expression,'".'])
   disp(' Available header mnemonics (besides "trace_no") are:')
   disp(cell2str(seismic.header_info(:,1),', '));
   error(' Abnormal termination')
end

                try
index=eval(['find(',lower(expression),')']);

                catch
disp([' The argument of keyword "traces" (',expression,')'])
disp(' is probably not a valid logical expression')
error(' Abnormal termination')

                end