# How to make streamline starting from the GM/WM interface to the pial suface

**URL:** <https://community.mrtrix.org/t/how-to-make-streamline-starting-from-the-gm-wm-interface-to-the-pial-suface/2396>\
**Category:** Uncategorized\
**Created:** [March 23, 2019, 12:02am UTC](https://community.mrtrix.org/t/how-to-make-streamline-starting-from-the-gm-wm-interface-to-the-pial-suface/2396 "2019-03-23T00:02:41Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Yixin\_Ma](https://community.mrtrix.org/user_avatar/community.mrtrix.org/yixin_ma/32/2696_2.png) [@Yixin\_Ma](https://community.mrtrix.org/u/Yixin_Ma)\
**Post date:** [March 23, 2019, 12:02am UTC](https://community.mrtrix.org/t/how-to-make-streamline-starting-from-the-gm-wm-interface-to-the-pial-suface/2396/1 "2019-03-23T00:02:41Z")

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Hi MRtrix3 experts,

I’m writing to ask about the streamline orientation. I want to track the fiber in cortical gray matter, ideally starting from the gray matter/ white matter interface to the pial surface. Now, I include only the cortex and generate a bunch of fibers. However, I cannot locate starting points and ending points (that saved in .tck file). That is to say, I don’t know if it’s close to the white matter or close to the CSF? Is there any tricks or function that I can use to achieve this?

For example, does the streamline always start from the seeding point? If that’s true, I can seed with GM/WM interface.

Best,

Yixin

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**Author:** ![rsmith](https://community.mrtrix.org/user_avatar/community.mrtrix.org/rsmith/32/2672_2.png) [@rsmith](https://community.mrtrix.org/u/rsmith)\
**Post date:** [April 6, 2019, 4:46pm UTC](https://community.mrtrix.org/t/how-to-make-streamline-starting-from-the-gm-wm-interface-to-the-pial-suface/2396/2 "2019-04-06T16:46:24Z")

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Hi Yixin,

The `.tck` format does _not_ store information regarding the seed point of each streamline; partly because the streamline should ideally not be highly dependent on which particular point along its length happened to be the seed point. However if you are performing _unidirectional_ tracking, then the _first_ vertex of each streamline is always the seed point. If you are doing bidirectional tracking, and absolutely must know the location of each streamline seed, you can use the [`-output_seeds` option](https://mrtrix.readthedocs.io/en/latest/reference/commands/tckgen.html#tractography-seeding-options-and-parameters).

Rob