Dear Paul,
I pre-processed my DTI data using afni and fatcat and output a trk data.
I met a problem to read in the trk data.
It seems that the "vox_to_ras" field is 0 in the trk output by 3dtrackID, which means "the matrix is not recorded" (http://www.trackvis.org/docs/?subsect=fileformat).
I would appreciate it if you can kindly check whether you had set the field correctly in the code of 3dTrackID.
The trk format is necessary for me as I want to use "tract_querier" tool to extract white matter structure. The "tract_querier" only accept the "trk" and "vtk" format (see [github.com]).
And I also use matlab to read in trk format to do some processing on the fiber level.

Thanks very much!
Best,
Lz