# EM modelling in cylindrical mesh

**URL:** <https://simpeg.discourse.group/t/em-modelling-in-cylindrical-mesh/74>\
**Category:** Electromagnetics\
**Created:** [February 20, 2020, 9:48am UTC](https://simpeg.discourse.group/t/em-modelling-in-cylindrical-mesh/74 "2020-02-20T09:48:32Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Alexey](https://avatars.discourse-cdn.com/v4/letter/a/47e85d/32.png) [@Alexey](https://simpeg.discourse.group/u/Alexey)\
**Post date:** [February 20, 2020, 9:48am UTC](https://simpeg.discourse.group/t/em-modelling-in-cylindrical-mesh/74/1 "2020-02-20T09:48:32Z")

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Hello,  
Is it necessary to give coincident horizontal coordinates of the receiver, source loop and mesh origin (r=0)? Or I can set some horizontal offsets for Tx and Rx? Will this be correct for calculations?

Alexey

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**Author:** ![lheagy](https://yyz2.discourse-cdn.com/free1/user_avatar/simpeg.discourse.group/lheagy/32/6_2.png) [@lheagy](https://simpeg.discourse.group/u/lheagy)\
**Post date:** [February 21, 2020, 11:34pm UTC](https://simpeg.discourse.group/t/em-modelling-in-cylindrical-mesh/74/2 "2020-02-21T23:34:49Z")

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Welcome @Alexey!

For the cylindrically symmetric mesh, the source loop does need to be centered at the origin in order to preserve cylindrical symmetry, but the receivers can be anywhere. For example, in [this notebook (FDEM\_vmd\_sounding\_over\_sphere.ipynb)](https://github.com/simpeg/em-notebooks/blob/master/notebooks/FDEM_vmd_sounding_over_sphere.ipynb), the receiver is offset from the transmitter by 8m.

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**Author:** ![subenyu](https://avatars.discourse-cdn.com/v4/letter/s/e19b73/32.png) [@subenyu](https://simpeg.discourse.group/u/subenyu)\
**Post date:** [February 22, 2020, 9:01am UTC](https://simpeg.discourse.group/t/em-modelling-in-cylindrical-mesh/74/3 "2020-02-22T09:01:35Z")

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> [@Alexey](#):
>
> source loop

hi where i can find the example of line source (horizontal electrical source )?  
thank you very much.

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**Author:** ![subenyu](https://avatars.discourse-cdn.com/v4/letter/s/e19b73/32.png) [@subenyu](https://simpeg.discourse.group/u/subenyu)\
**Post date:** [February 22, 2020, 9:02am UTC](https://simpeg.discourse.group/t/em-modelling-in-cylindrical-mesh/74/4 "2020-02-22T09:02:38Z")

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> [@subenyu](#):
>
> hi where i can find the example of line source (horizontal electrical source )?  
> thank you very much

@lheagy hi thank you very much.  
hi where i can find the example of line source (horizontal electrical source )?  
thank you very much