# Understanding strike\_dir output from PyLith

**URL:** <https://community.geodynamics.org/t/understanding-strike-dir-output-from-pylith/1564>\
**Category:** PyLith\
**Created:** [November 3, 2020, 4:12pm UTC](https://community.geodynamics.org/t/understanding-strike-dir-output-from-pylith/1564 "2020-11-03T16:12:39Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![josimar](https://avatars.discourse-cdn.com/v4/letter/j/cab0a1/32.png) [@josimar](https://community.geodynamics.org/u/josimar)\
**Post date:** [November 3, 2020, 4:12pm UTC](https://community.geodynamics.org/t/understanding-strike-dir-output-from-pylith/1564/1 "2020-11-03T16:12:39Z")

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Hi @baagaard and @willic3

I would like to understand better the output `strike_dir` from PyLith. This output is found on the files fault\_info.h5 for example.

In the PyLith manual it says that `strike_dir` is the “Direction of fault strike in global coordinate system”.

In the example below I show a fault plane that is perpendicular to the x-direction. The field `strike_dir` that is output from PyLith contains 3 components. I am trying to wrap my mind about this information:

1. The output from `strike_dir` are in radians, correct?

2. In the figure below, why is the x-component of the `strike_dir` output equal to -0.17? Assuming that this is radians, this would correspond to -9 degrees. Shouldn’t it be 90 degrees ?

3. The y-components is equal zero, which make sense in this case, right?

4. Why is the z-component equal to -0.98, which in is ~56 degrees?

Thank you in advance for the help.  
Josimar

 ![Screen Shot 2020-11-03 at 10.58.13 AM](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/1X/8239c7110778e34d6fd72e5d61d0fd09cdcd0d1b.jpeg)

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**Author:** ![baagaard](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/baagaard/32/615_2.png) [@baagaard](https://community.geodynamics.org/u/baagaard)\
**Post date:** [November 3, 2020, 6:10pm UTC](https://community.geodynamics.org/t/understanding-strike-dir-output-from-pylith/1564/2 "2020-11-03T18:10:15Z")

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The components of strike\_dir, dip\_dir, and fault\_normal are the direction cosines of the vectors pointing in the along-strike direction, up-dip direction, and fault normal direction in the global coordinate system. As discussed in the manual and examples, you can use these to transform the fault output given in the local fault coordinate system to the global coordinate system.