function [fld]=read_bin(fileName,varargin);
%usage: fld=read_bin(fileName);         reads 3D field (N levels in 3rd dim)
%usage: fld=read_bin(fileName,trec);    reads 3D field, at trec (50 levels)  
%usage: fld=read_bin(fileName,trec,k);  reads 2D field, at level k, at trec (50 levels)
%usage: fld=read_bin(fileName,trec,0);  reads 2D field, at trec (1 level)
%usage: fld=read_bin(fileName,trec,0,prec); prec can be set to 32 (default) or 64 (double precision)

gcmfaces_global;

if nargin>1; tt=varargin{1}; else; tt=1; end;
if nargin>2; kk=varargin{2}; else; kk=[]; end;
if nargin>3; prec=varargin{3}; else; prec=32; end;

myprec=['float' num2str(prec)];
n1=mygrid.ioSize(1); n2=mygrid.ioSize(2); n3=length(mygrid.RC); nF=mygrid.nFaces;
recl2D=n1*n2*(prec/8); recl3D=n1*n2*n3*(prec/8);

if nargin==1; n3=dir(fileName); n3=n3.bytes/recl2D; recl3D=recl2D*n3; end;

fid=fopen(fileName,'r','b');
if ~isempty(kk);
  if kk==0;%meaning the field is only two dimensional
      status=fseek(fid,(tt-1)*recl2D,'bof');
      fld=reshape(fread(fid,n1*n2,myprec),[n1 n2]);
  else;
      status=fseek(fid,(tt-1)*recl3D+(kk-1)*recl2D,'bof');
      fld=reshape(fread(fid,n1*n2,myprec),[n1 n2]);
  end;
else;
  status=fseek(fid,(tt-1)*recl3D,'bof');
  fld=reshape(fread(fid,n1*n2*n3,myprec),[n1 n2 n3]);
end;
fclose(fid);

fld=convert2gcmfaces(fld);