Hi Mahmoud,
I’m not sure I understand the question right. You say you want to replace the position coordinates with an ROI, but those position coordinates are a ROI. My guess is that by ROI you mean a binary mask? In that case, it’s really easy to use the tckedit command with such a binary mask. You can directly provide that image to tckedit, e.g. (assuming your binary mask is called “roiMask.mif” and your desired output “roi.tck”):
tckedit -include roiMask.mif sift_1mio.tck roi.tck
Hope that helps.
Best,
Marlene