# Error computing orientation of cell face

**URL:** <https://community.geodynamics.org/t/error-computing-orientation-of-cell-face/1772>\
**Category:** PyLith\
**Created:** [April 1, 2021, 12:32pm UTC](https://community.geodynamics.org/t/error-computing-orientation-of-cell-face/1772 "2021-04-01T12:32:54Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![RanXu](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@RanXu](https://community.geodynamics.org/u/RanXu)\
**Post date:** [April 1, 2021, 12:32pm UTC](https://community.geodynamics.org/t/error-computing-orientation-of-cell-face/1772/1 "2021-04-01T12:32:54Z")

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Hello  
I divided the surface into several fault plane and assigned different friction parameters. the nodesets and sidesets are shown in the figure below. ![nodesets](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/1X/052085615cebf356b2d1bcded3009d1e5fb04705.png) ![sidesets](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/1X/63bb604ae3722f1bd83b84df098196b349e1ce63.png) . when i give some change for code of 3d/hex8/step13 ,It has the following error and exits

 ![exit](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/1X/f04b355ece53b630304d63b05fea6aeccc8bd696.png) .  
thanks  
ran

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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:** [April 1, 2021, 2:17pm UTC](https://community.geodynamics.org/t/error-computing-orientation-of-cell-face/1772/2 "2021-04-01T14:17:17Z")

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It appears that you have a horizontal fault surface (x-y plane). See `up_dir` in Section 6.4.3 of the PyLith v2.2.2 manual. The first fault tangential direction is `up_dir x fault_normal` and the second fault tangential direction is `fault_normal x first_tangential_dir`. In order to define the first tangential direction you must specify an `up_dir` that is not collinear with the fault normal direction. The default is `[0,0,1]` which works as long as the fault surface is not horizontal (x-y plane).

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**Author:** ![RanXu](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@RanXu](https://community.geodynamics.org/u/RanXu)\
**Post date:** [April 4, 2021, 2:14am UTC](https://community.geodynamics.org/t/error-computing-orientation-of-cell-face/1772/3 "2021-04-04T02:14:51Z")

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Yeah, it works when I change my up-dir to (1,1,0), \* But I think all six of my faults are in the X-Z plane.

 ![1](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/1X/f69f1d348cbae883029ca776b3eeb18c021e0813.png)

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<div class="post-metadata">

**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:** [April 4, 2021, 2:29am UTC](https://community.geodynamics.org/t/error-computing-orientation-of-cell-face/1772/4 "2021-04-04T02:29:18Z")

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You can also get this error if you have faults with buried edges and forget to set them accordingly. See figures 6.3 and 6.4 in the PyLith v2.2.1 or v2.2.2 manual.

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<div class="post-metadata">

**Author:** ![RanXu](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@RanXu](https://community.geodynamics.org/u/RanXu)\
**Post date:** [April 4, 2021, 1:19pm UTC](https://community.geodynamics.org/t/error-computing-orientation-of-cell-face/1772/5 "2021-04-04T13:19:16Z")

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yeah,it works when i reset buried edges.thank you!