# Select nc variables for pygmt

**URL:** <https://forum.generic-mapping-tools.org/t/select-nc-variables-for-pygmt/2160>\
**Category:** PyGMT Q&A\
**Created:** [October 1, 2021, 11:58pm UTC](https://forum.generic-mapping-tools.org/t/select-nc-variables-for-pygmt/2160 "2021-10-01T23:58:41Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![yangleir](https://avatars.discourse-cdn.com/v4/letter/y/a8b319/32.png) [@yangleir](https://forum.generic-mapping-tools.org/u/yangleir)\
**Post date:** [October 1, 2021, 11:58pm UTC](https://forum.generic-mapping-tools.org/t/select-nc-variables-for-pygmt/2160/1 "2021-10-01T23:58:42Z")

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Hi,all  
I need to plot nc formatted grid files which contain some different variables. How to select the one I needed to plot using grdimage?  
I tried the `ncfilename?var`, but it did not work.

Lei

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<div class="post-metadata">

**Author:** ![weiji14](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/weiji14/32/33_2.png) [@weiji14](https://forum.generic-mapping-tools.org/u/weiji14)\
**Post date:** [October 2, 2021, 7:05am UTC](https://forum.generic-mapping-tools.org/t/select-nc-variables-for-pygmt/2160/2 "2021-10-02T07:05:09Z")

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The `ncfilename?var` method should work. Could you post the output of `gmt grdinfo ncfilename` and `gdalinfo ncfilename` so we can look at the NetCDF metadata?

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<div class="post-metadata">

**Author:** ![yangleir](https://avatars.discourse-cdn.com/v4/letter/y/a8b319/32.png) [@yangleir](https://forum.generic-mapping-tools.org/u/yangleir)\
**Post date:** [October 2, 2021, 10:27am UTC](https://forum.generic-mapping-tools.org/t/select-nc-variables-for-pygmt/2160/3 "2021-10-02T10:27:28Z")

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Thanks.

I got the reason now. The `var` should not set like:

```auto
fig.grdimage(grid=grid?var,projection="Cyl_stere/150/-20/15c", region="g")

```

Instead, it should be:

```auto
grid = 'ncfilename?var'
fig.grdimage(grid=grid,projection="Cyl_stere/150/-20/15c", region="g")

```

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<div class="post-metadata">

**Author:** ![weiji14](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/weiji14/32/33_2.png) [@weiji14](https://forum.generic-mapping-tools.org/u/weiji14)\
**Post date:** [October 3, 2021, 10:46am UTC](https://forum.generic-mapping-tools.org/t/select-nc-variables-for-pygmt/2160/4 "2021-10-03T10:46:25Z")

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Yep, and just for future reference, the relevant GMT documentation page is at [https://docs.generic-mapping-tools.org/6.2/cookbook/features.html#modifiers-for-coards-compliant-netcdf-files](https://docs.generic-mapping-tools.org/6.2/cookbook/features.html#modifiers-for-coards-compliant-netcdf-files). The `ncfilename?var` syntax is for 2-D NetCDF files, but apparently you can do more complicated selections on 3-D and 4-D NetCDF files too using e.g. `ncfilename?var[1]` or `ncfilename?var[1,2]`. Might come in handy someday!