The problem appears when stacking the two datasets.
the node_indices are as follow...
>> ds_left_right.fa.node_indices
ans =
1 2 3 4 5 6 13 14 15 16 17 18
Thus, when trying to save the dset, the cosmo_map2surface function reports the next problem
>> cosmo_map2surface(ds_left_right, 'test_data');
Error using cosmo_check_dataset (line 137)
: .fa.node_indices must be vector with integers in range 1..12
Error in cosmo_map2surface (line 89)
cosmo_check_dataset(ds,'surface');
I have taking a better look of the code and I think that the problem is in here
offset_left=numel(ds_left.a.fdim.values{index}); %(which is 12)
and it should be:
offset_left=numel(ds_left.fa.node_indices); %(which is 6)
After changing this, everything works correctly. See below:
% generate synthetic left and right hemisphere data
% (this is just example data for illustration)
ds_left=cosmo_synthetic_dataset('type','surface','seed',1);
ds_right=cosmo_synthetic_dataset('type','surface','seed',2);
% Set the number of vertices of the left surface.
% If the surface is sparse (it does not have data for all nodes), it *may*
% be necessary to adjust this value manually. In that case, consider to:
%
% - compute the number of vertices, if it is a standardized surface from
% MapIcosahedron. If the ld parameter was set to 64, then the number of
% vertices is 10*64^2+2=40962.
% - get the number of vertices using:
% [v,f]=surfing_read('left_surface.asc');
% nverts=max(size(v));
%
[unused, index]=cosmo_dim_find(ds_left, 'node_indices');
nverts_left=max(ds_left.a.fdim.values{index});
% update node indices to support indexing data from two hemispheres
node_indices=[ds_left.a.fdim.values{index}, ...
nverts_left+ds_right.a.fdim.values{index}];
ds_left.a.fdim.values{index}=node_indices;
ds_right.a.fdim.values{index}=node_indices;
% update node indices for right hemisphere
ds_left.fa.node_indices
offset_left=numel(ds_left.fa.node_indices);
assert(all(ds_left.fa.node_indices<=offset_left)); % safety check
ds_right.fa.node_indices=ds_right.fa.node_indices +offset_left;
% merge hemisphes
ds_left_right=cosmo_stack({ds_left,ds_right},2);
