# Plot wind vectors from a XArray DataArray **URL:** \ **Category:** PyGMT Q&A\ **Created:** [November 2, 2020, 8:21pm UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002 "2020-11-02T20:21:19Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![jdassink](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/jdassink/32/673_2.png) [@jdassink](https://forum.generic-mapping-tools.org/u/jdassink)\ **Post date:** [November 2, 2020, 8:21pm UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/1 "2020-11-02T20:21:19Z")
Hi! I am trying to plot temperature and wind data from a Xarray data array. To show what I want to achieve, I have attached an example Matplotlib plot and a GMT plot that somewhat mimics it, here still without the wind vectors. The plot is made with GMT 6.1.1 and pygmt 0.2.0. I am getting stuck trying to plot the wind vectors. How should I proceed in pygmt? I tried: ```auto u=ds.u.isel(isobaricInhPa=0) v=ds.v.isel(isobaricInhPa=0) fig.plot(lons.values, lats.values, direction=[u.values, v.values], style='V') ``` which yields: ```auto --------------------------------------------------------------------------- GMTInvalidInput Traceback (most recent call last) in 36 fig.coast(projection=PROJECTION, region=REGION, frame="g", land="gray") 37 fig.grdimage(windspeed.isel(isobaricInhPa=0), n='b', Q=True) ---> 38 fig.plot(lons.values, lats.values, direction=[u.values, v.values], style='V') 39 fig.coast(projection=PROJECTION, region=REGION, frame="g", shorelines=True) 40 fig.text(position='BL',text='d.', font=label_font) ~/opt/miniconda3/envs/pygmt/lib/python3.6/site-packages/pygmt/helpers/decorators.py in new_module(*args, **kwargs) 235 if alias in kwargs: 236 kwargs[arg] = kwargs.pop(alias) --> 237 return module_func(*args, **kwargs) 238 239 new_module.aliases = aliases ~/opt/miniconda3/envs/pygmt/lib/python3.6/site-packages/pygmt/helpers/decorators.py in new_module(*args, **kwargs) 372 kwargs[arg] = separators[fmt].join(f"{item}" for item in value) 373 # Execute the original function and return its output --> 374 return module_func(*args, **kwargs) 375 376 return new_module ~/opt/miniconda3/envs/pygmt/lib/python3.6/site-packages/pygmt/base_plotting.py in plot(self, x, y, data, sizes, direction, **kwargs) 561 ) 562 --> 563 with file_context as fname: 564 arg_str = " ".join([fname, build_arg_string(kwargs)]) 565 lib.call_module("plot", arg_str) ~/opt/miniconda3/envs/pygmt/lib/python3.6/contextlib.py in __enter__ (self) 79 def __enter__ (self): 80 try: ---> 81 return next(self.gen) 82 except StopIteration: 83 raise RuntimeError("generator didn't yield") from None ~/opt/miniconda3/envs/pygmt/lib/python3.6/site-packages/pygmt/clib/session.py in virtualfile_from_vectors(self, *vectors) 1160 rows = len(arrays[0]) 1161 if not all(len(i) == rows for i in arrays): -> 1162 raise GMTInvalidInput("All arrays must have same size.") 1163 1164 family = "GMT_IS_DATASET|GMT_VIA_VECTOR" GMTInvalidInput: All arrays must have same size. ``` Any help would be greatly appreciated! Jelle p.s. the `fig.plot()` is part of a larger pygmt call, for context: ```auto label_font = '14p,Helvetica-Bold,black' REGION = 'g' PROJECTION = 'G-35/60/8c' # Figuur D fig.coast(projection=PROJECTION, region=REGION, frame="g", land="gray") fig.grdimage(windspeed.isel(isobaricInhPa=0), n='b', Q=True) fig.plot(lons.values, lats.values, direction=[u.values, v.values], style='V') fig.coast(projection=PROJECTION, region=REGION, frame="g", shorelines=True) fig.text(position='BL',text='d.', font=label_font) ``` ![temperature-wind-pl](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/5c1eef62052968054c5fe5f1f2221729a76d8a74.jpeg) ![ecmwf_gmt](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/2825e7f27da62726685b93ade770740669515b8e.png) ---
**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:** [November 3, 2020, 9:21am UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/2 "2020-11-03T09:21:32Z")
Hi @jdassink, welcome to the GMT forum! I’m not too familiar with plotting velocity vectors, but the `GMTInvalidInput` error message you’re getting indicates that your arrays (`lons`, `lats`, `u` and `v`) are probably of different lengths. Perhaps do a `print(len(lons.values), len(lats.values), len(u.values), len(v.values))` and see if they are the same. If not, maybe upload a sample of your `xarray.DataArray` (e.g. as a zipped NetCDF file) so that we can take a look at what’s wrong? As an aside, if you want to get the pointy colorbar like in the matplotlib plot, do `fig.colorbar(position="JBC+e")` (key is the `+e` which adds sidebar triangles). See also [https://docs.generic-mapping-tools.org/latest/colorbar.html#d](https://docs.generic-mapping-tools.org/latest/colorbar.html#d). P.S. There’s a PR in progress for `velo` at [https://github.com/GenericMappingTools/pygmt/pull/525](https://github.com/GenericMappingTools/pygmt/pull/525) which may be of interest if you need to plot more complicated velocity vectors (e.g. with error ellipses and annotations). ---
**Author:** ![jdassink](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/jdassink/32/673_2.png) [@jdassink](https://forum.generic-mapping-tools.org/u/jdassink)\ **Post date:** [November 12, 2020, 5:48pm UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/3 "2020-11-12T17:48:38Z")
Hi @weiji14, thanks for your answer. I tried a bit more and decided to use `grdvector` by using the GMT clib directly. I advanced a bit in my figure, and now am almost able to produce what I want. Basically the call that is use is: ```auto fig.coast(projection=PROJECTION, region=REGION, frame="g", land="gray") fig.grdimage(windspeed.isel(isobaricInhPa=0), n='b', Q=True) fig.coast(projection=PROJECTION, region=REGION, frame="g", shorelines=True) ds.u.isel(isobaricInhPa=0).to_netcdf('u.grd') ds.v.isel(isobaricInhPa=0).to_netcdf('v.grd') with pygmt.clib.Session() as session: session.call_module('grdvector', f'u.grd v.grd -I10d/10d -Gwhite -Q0.1i+e+gwhite -W0.8p,black -Si0.1d') fig.text(position='BL',text='d.', font=label_font) ``` and so forth for the other subfigures. I get the following plot: ![gmt_20201112](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/3949c856a88516858018c379b64f15a4be460613.jpeg) It shows these weird effects around the poles. Any idea? ---
**Author:** ![thomas.schouten](https://avatars.discourse-cdn.com/v4/letter/t/7ab992/32.png) [@thomas.schouten](https://forum.generic-mapping-tools.org/u/thomas.schouten)\ **Post date:** [May 25, 2022, 9:20am UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/4 "2022-05-25T09:20:21Z")
Hi! I have been having the same error message (`GMTInvalidInput: All arrays must have same size`). I checked the length of each array and they are equal: ![image](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/2X/b/b9411005fa4b7c06407e4ac5fc226dd4c1157e24.png) Here is what I try to do: ``` fig = pygmt.Figure() fig.basemap(region=region, projection=proj, frame=True) fig.grdimage("ETOPO1_Ice_g_geotiff.tif", projection=proj, frame=True, cmap="oleron") fig.colorbar(frame='af+l"Topography (m)"') fig.plot( x=lon, y=lat, direction=[[azi],[mag]], style="V", pen="1p", color="black", ) fig.savefig("tectonics_map.png") fig.show() ``` Many thanks! ---
**Author:** ![Joaquim](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/joaquim/32/16_2.png) [@Joaquim](https://forum.generic-mapping-tools.org/u/Joaquim)\ **Post date:** [May 25, 2022, 11:10am UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/5 "2022-05-25T11:10:20Z")
> [@thomas.schouten](#): > > `direction=[[azi],[mag]]` Despite my PyIgnorance I strongly suspect of the above line ---
**Author:** ![thomas.schouten](https://avatars.discourse-cdn.com/v4/letter/t/7ab992/32.png) [@thomas.schouten](https://forum.generic-mapping-tools.org/u/thomas.schouten)\ **Post date:** [May 25, 2022, 11:11am UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/6 "2022-05-25T11:11:06Z")
Hi Joaquim! Would you have any suggestion how I should code this instead? Thanks! Thomas ---
**Author:** ![Joaquim](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/joaquim/32/16_2.png) [@Joaquim](https://forum.generic-mapping-tools.org/u/Joaquim)\ **Post date:** [May 25, 2022, 11:29am UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/7 "2022-05-25T11:29:49Z")
Sure, remove that trouble-maker " : " from file. EDIT: hoops, we are mixing the threads. ---
**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:** [May 25, 2022, 2:27pm UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/8 "2022-05-25T14:27:21Z")
Hmm, looking at [https://www.pygmt.org/v0.6.1/api/generated/pygmt.Figure.plot.html](https://www.pygmt.org/v0.6.1/api/generated/pygmt.Figure.plot.html), I’m guessing that you should do `direction=[azi, mag]` instead? What type of Python objects are `azi` and `mag`? ---
**Author:** ![thomas.schouten](https://avatars.discourse-cdn.com/v4/letter/t/7ab992/32.png) [@thomas.schouten](https://forum.generic-mapping-tools.org/u/thomas.schouten)\ **Post date:** [May 27, 2022, 8:45am UTC](https://forum.generic-mapping-tools.org/t/plot-wind-vectors-from-a-xarray-dataarray/1002/9 "2022-05-27T08:45:53Z")
Fixed it! I needed to plot it as `direction=[azi, mag]` indeed. Also, my angles were in radians, not degrees, so that’s why I kept running into the problem of only north-facing vectors when it did work 😅