function a = mk3D(b,c)

a=c;

if isa(b,'gcmfaces');
   %go from 2D field to 3D field
      n3=size(a.f1,3);
      for iFace=1:a.nFaces;
         iF=num2str(iFace);
         eval(['tmp1=b.f' iF ';']); [n1,n2]=size(tmp1); tmp1=tmp1(:); 
         tmp1=tmp1*ones(1,size(a.f1,3)); tmp1=reshape(tmp1,[n1 n2 n3]);
         eval(['a.f' iF '=tmp1;']);
      end;
elseif isa(b,'double');
      n3=length(b);
      if size(b,1)~=1; b=b'; end;
      for iFace=1:a.nFaces;   
         iF=num2str(iFace);
         eval(['tmp1=c.f' iF ';']); tmp2=size(tmp1); n1=tmp2(1); n2=tmp2(2);
         tmp1=reshape(ones(n1*n2,1)*b,[n1 n2 n3]);;
         eval(['a.f' iF '=tmp1;']);
      end;
else
   error('indexing not supported by gcmfaces objects')
end