For the -fwhm_tck option for tckmap, how are the voxels handled that correspond to the end of tracks?
Firstly, to be clear, the operation underlying the
-fwhm_tck option does not operate on voxels; it operates on the streamline itself. Whatever quantitative value is derived per vertex is smoothed based on the distances between vertices; it is only once each vertex is then mapped to a voxel that this smoothed value “comes along for the ride” in order to contribute appropriately to the final image.
So following this, at the streamline endpoints (not the voxels they are assigned to), the smoothing kernel that is centred at that vertex simply has half of the kernel truncated, so looks like a half-normal distribution, The resulting values are still smooth rather than decreasing in magnitude toward the streamline ends, because the integral of the applied kernel is used to normalise the resulting value at each vertex code.
Hope that answers your question; there’s bits in there that don’t quite make sense to me, so if there’s something out standing you might need to try to rephrase.