.. DO NOT EDIT. .. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY. .. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE: .. "examples/plot-vector-methods.py" .. LINE NUMBERS ARE GIVEN BELOW. .. only:: html .. note:: :class: sphx-glr-download-link-note :ref:`Go to the end ` to download the full example code. .. rst-class:: sphx-glr-example-title .. _sphx_glr_examples_plot-vector-methods.py: ======================= Vector plotting methods ======================= To plot vector quantities such as currents we can use a quiver plot in matplotlib. In the `GBR4` tutorial dataset the u and v variables contain the x and y components of the vector for each cell in the dataset. .. GENERATED FROM PYTHON SOURCE LINES 11-27 .. code-block:: Python import matplotlib.pyplot as plt import numpy import pandas import xarray from shapely import box import emsarray from emsarray import plot from emsarray.operations import point_extraction dataset = emsarray.tutorial.open_dataset('gbr4') surface_currents = dataset.ems.select_variables(["temp", "u", "v"]).isel(time=0, k=-1) surface_currents.load() .. raw:: html 
<xarray.Dataset> Size: 4MB
    Dimensions:    (j: 180, i: 600)
    Coordinates:
        latitude   (j, i) float64 864kB -8.074 -8.107 -8.139 ... -28.56 -28.59
        longitude  (j, i) float64 864kB 142.2 142.2 142.2 ... 156.9 156.9 156.9
        time       datetime64[ns] 8B 2022-10-15T14:00:00
        zc         float64 8B 1.5
    Dimensions without coordinates: j, i
    Data variables:
        temp       (j, i) float64 864kB nan nan nan nan ... 20.9 20.92 20.93 20.93
        u          (j, i) float64 864kB nan nan nan ... -0.005159 0.03509 0.05466
        v          (j, i) float64 864kB nan nan nan nan ... 0.08804 0.08797 0.04464
    Attributes: (12/16)
        title:                           gbr4_H4p0_ABARRAr2_OBRAN2020_FG2Gv3_Dhnd
        description:                     eReefs GBR 4k grid with 64 active river ...
        paramhead:                       eReefs GBR 4k grid, with Atmospheric for...
        paramfile:                       /g/data/et4/projects/eReefs/gbr4_H4p0_AB...
        ems_version:                     v1.4.0 rev(7365)
        date_created:                    Mon Oct 21 15:47:23 2024
        ...                              ...
        bald__isPrefixedBy:              prefix_list
        metadata_link:                   https://marlin.csiro.au/geonetwork/srv/e...
        prefix_list_puv__:               https://w3id.org/env/puv#
        DODS_EXTRA.Unlimited_Dimension:  time
        history:                         Wed Jan 14 14:15:20 2026: ncks -d time,0...
        NCO:                             netCDF Operators version 5.3.6 (Homepage...


.. GENERATED FROM PYTHON SOURCE LINES 28-29 Plotting every cell is straight forward for small areas: .. GENERATED FROM PYTHON SOURCE LINES 30-52 .. code-block:: Python figure = plt.figure(figsize=(7, 8), layout="constrained") axes = figure.add_subplot(projection=dataset.ems.data_crs) figure.suptitle("Surface water temperature and currents near the Whitsundays") temp = surface_currents["temp"] temp_artist = dataset.ems.make_artist( axes, temp, cmap="coolwarm", clim=(24, 27)) current_artist = dataset.ems.make_artist( axes, (surface_currents["u"], surface_currents["v"]), scale=20, scale_units="width") plot.add_coast(axes) plot.add_gridlines(axes) # Just show a small area over the Whitsundays view_box = box(148.7, -20.4, 149.6, -19.8) axes.set_aspect("equal", adjustable="datalim") axes.set_extent(plot.bounds_to_extent(view_box.bounds)) .. image-sg:: /examples/images/sphx_glr_plot-vector-methods_001.png :alt: Surface water temperature and currents near the Whitsundays :srcset: /examples/images/sphx_glr_plot-vector-methods_001.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 53-54 Plotting the entire dataset this way leads to the current vectors becoming a confusing mess however: .. GENERATED FROM PYTHON SOURCE LINES 55-74 .. code-block:: Python figure = plt.figure(figsize=(7, 10), layout="constrained") axes = figure.add_subplot(projection=dataset.ems.data_crs) figure.suptitle("A bad plot of surface water temperature and currents over the entire reef") temp = surface_currents["temp"] temp_artist = dataset.ems.make_artist(axes, temp, cmap="coolwarm") current_artist = dataset.ems.make_artist( axes, (surface_currents["u"], surface_currents["v"]), scale=20, scale_units="width") plot.add_coast(axes) plot.add_gridlines(axes) # Show the entire model domain axes.set_aspect("equal", adjustable="datalim") axes.autoscale() .. image-sg:: /examples/images/sphx_glr_plot-vector-methods_002.png :alt: A bad plot of surface water temperature and currents over the entire reef :srcset: /examples/images/sphx_glr_plot-vector-methods_002.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 75-83 Sampling gridded datasets ========================= For datasets on a two dimensional grid like this we can sample the current data at regular intervals to display only a subset of the vectors. The sampled points will follow the geometry of the dataset. For curvilinear datasets such as `GBR4` the vectors will follow the curves of the dataset shape: .. GENERATED FROM PYTHON SOURCE LINES 84-117 .. code-block:: Python # Make an empty array of the same shape as the data, then select every 10th cell in there. face_grid = dataset.ems.get_grid(surface_currents["u"]) samples = xarray.DataArray(numpy.full(face_grid.size, False)) samples = face_grid.wind(samples) samples[::10, ::10] = True samples = dataset.ems.ravel(samples) # Select the (x, y) coordinates and the (u, v) components of the sampled cells x, y = face_grid.centroid_coordinates[samples].T u = dataset.ems.ravel(surface_currents["u"]).values[samples] v = dataset.ems.ravel(surface_currents["v"]).values[samples] # Plot the points figure = plt.figure(figsize=(7, 10), layout="constrained") axes = figure.add_subplot(projection=dataset.ems.data_crs) figure.suptitle("Surface water temperature and currents across the entire dataset domain") temp = surface_currents["temp"] temp_artist = dataset.ems.make_artist(axes, temp, cmap="coolwarm") quiver = plt.quiver( x, y, u, v, scale=40, scale_units="width") axes.add_collection(quiver) plot.add_coast(axes) plot.add_gridlines(axes) # Show the entire model domain axes.set_aspect("equal", adjustable="datalim") axes.autoscale() .. image-sg:: /examples/images/sphx_glr_plot-vector-methods_003.png :alt: Surface water temperature and currents across the entire dataset domain :srcset: /examples/images/sphx_glr_plot-vector-methods_003.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 118-126 Sampling the dataset domain =========================== Another approach is to plot vectors at regular points across the dataset domain by sampling at regular intervals. The vector locations are not tied to the grid geometry. This approach will work with unstructured grids unlike the previous method. :func:`.point_extraction.extract_dataframe` can be used for this: .. GENERATED FROM PYTHON SOURCE LINES 127-160 .. code-block:: Python # Generate a mesh of points across the dataset domain domain = box(*dataset.ems.bounds) x = numpy.arange(domain.bounds[0], domain.bounds[2], 0.4) y = numpy.arange(domain.bounds[1], domain.bounds[3], 0.4) xx, yy = numpy.meshgrid(x, y) points = pandas.DataFrame({ 'x': xx.flatten(), 'y': yy.flatten(), }) # Extract the surface current components at these locations components = point_extraction.extract_dataframe( surface_currents, points, ('x', 'y'), missing_points='drop') # Plot the points figure = plt.figure(figsize=(7, 10), layout="constrained") axes = figure.add_subplot(projection=dataset.ems.data_crs) figure.suptitle("Surface water temperature and currents across the entire dataset domain") temp = surface_currents["temp"] temp_artist = dataset.ems.make_artist(axes, temp, cmap="coolwarm") quiver = plt.quiver( components['x'], components['y'], components['u'], components['v'], scale=30, scale_units="width") axes.add_collection(quiver) plot.add_coast(axes) plot.add_gridlines(axes) axes.set_aspect("equal", adjustable="datalim") axes.autoscale() .. image-sg:: /examples/images/sphx_glr_plot-vector-methods_004.png :alt: Surface water temperature and currents across the entire dataset domain :srcset: /examples/images/sphx_glr_plot-vector-methods_004.png :class: sphx-glr-single-img .. rst-class:: sphx-glr-timing **Total running time of the script:** (0 minutes 14.574 seconds) .. _sphx_glr_download_examples_plot-vector-methods.py: .. only:: html .. container:: sphx-glr-footer sphx-glr-footer-example .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: plot-vector-methods.ipynb ` .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: plot-vector-methods.py ` .. container:: sphx-glr-download sphx-glr-download-zip :download:`Download zipped: plot-vector-methods.zip ` .. only:: html .. rst-class:: sphx-glr-signature `Gallery generated by Sphinx-Gallery `_