Hi @FEHildesheim,
I had a quick look into this, and as far as I can tell, the issue is with the trailing commas left behind in your seeds.txt file (judging from the command you sent me privately). Try this command instead:
awk -F, '!/^#/ { print $3,$4,$5; }' < tckgen_seeds.txt > seed_coords.txt
Then the tckconvert call should work:
tckconvert seed_coords.txt seeds.tck
You should then be able to load this file into mrview, and set the geometry to ‘points’ – along with the original tractogram if desired.
Here’s an example on my system
Cheers,
Donald.