Re: [Gwyddion-users] Reading .gwy files into Matlab

[Lennart Fricke]

I've created a simple script that can import the data fields of Gwyddion
files into Matlab.

It works for me, but does not give you the units.

Regards
Lennart


% Copyright © 2011, Lennart Fricke
%
% E-Mail: lennart.fri...@kabelmail.de
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the BSD 2-Clause License.
% 
% 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
% BSD 2-Clause License for more details.
% 
% You should have received a copy of the BSD 2-Clause License
% along with this program.
function channel = readgwychannel(filename,chno)
% Get Channel with number cno from a Gwyddion File
% returns a struct containing data and additional information
% chno is the channel number (starting at 0)
  channel = 0;
  title = 0;
  cname = sprintf('/%u/data',chno);
  fid = fopen(filename);
  c = transpose(fread(fid,4,'*char'));
  if ~strcmp(c,'GWYP')
      return
  end
  t = readobj(fid);
  if ~strcmp(t,'GwyContainer')
      return;
  end
  [n,t,ret] = readcomponent(fid);
  while ~feof(fid)
      if t=='o'
          [t,s] = readobj(fid);
          if ~strcmp(n,cname)
              fseek(fid,s,'cof');
          else
              channel = readdatafield(fid,s);
              if ischar(title)
                  channel.title = title;
                  return
              end
          end
      elseif t=='s' && strcmp(n,[cname, '/title'])
          title = ret;
          if isstruct(channel)
              channel.title = title;
              return
          end
      end
      [n,t,ret] = readcomponent(fid);
  end
end

function rfield = readdatafield(fid,size)
   p = ftell(fid);
   while ftell(fid)<size+p
      [n,t,r] = readcomponent(fid);
      if t~='o'
        rfield.(n) = r;
      else
        [t,s] = readobj(fid);
        fseek(fid,s,'cof');
      end
   end
   rfield.data=transpose(reshape(rfield.data,rfield.xres,rfield.yres));
end
function [s] = readstr(fid)
  s = blanks(100);
  c = fread(fid,1,'*char');
  count = 1;
  while ~feof(fid) && c~=0 && count<100
      s(count) = c;
      c = fread(fid,1,'*char');
      count = count+1;
  end
  if count>1
      s = s(1:count-1);
  else
      s=0;
  end
end  

function [type,size] = readobj(fid)
  type = readstr(fid);
  size = fread(fid,1,'uint32','l');
end

function [name, type, ret] = readcomponent(fid)
    name = readstr(fid);
    type = fread(fid,1,'*char');
    if feof(fid) 
        ret = 0;
        return
    end
    switch lower(type)
        case 'b'
            r = '*uint8';
        case 'c'
            r = '*char';
        case 'i'
            r = '*int32';
        case 'q'
            r = '*int64';
        case 'd'
            r = '*double';
        case {'s', 'o'}
            r = 0;
    end
    if isstrprop(type,'upper')
        rep = fread(fid,1,'uint32','l');
    else
        rep = 1;
    end
    if r ~= 0
        ret = fread(fid,rep,r,'l');
    elseif lower(type)=='s'
        ret = cell(rep);
        for i=1:rep
            ret{i}=readstr(fid);
        end
    else
        ret = 0;
    end
    type = lower(type);        
end
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