.. note::
    :class: sphx-glr-download-link-note

    Click :ref:`here <sphx_glr_download_gallery_regridding_arrows.py>` to download the full example code
.. rst-class:: sphx-glr-example-title

.. _sphx_glr_gallery_regridding_arrows.py:


Regridding vectors with quiver
------------------------------

This example demonstrates the regridding functionality in quiver (there exists
equivalent functionality in :meth:`cartopy.mpl.geoaxes.GeoAxes.barbs`).

Regridding can be an effective way of visualising a vector field, particularly
if the data is dense or warped.





.. image:: /gallery/images/sphx_glr_regridding_arrows_001.png
    :class: sphx-glr-single-img





.. code-block:: python


    import matplotlib.pyplot as plt
    import numpy as np

    import cartopy.crs as ccrs


    def sample_data(shape=(20, 30)):
        """
        Return ``(x, y, u, v, crs)`` of some vector data
        computed mathematically. The returned CRS will be a North Polar
        Stereographic projection, meaning that the vectors will be unevenly
        spaced in a PlateCarree projection.

        """
        crs = ccrs.NorthPolarStereo()
        scale = 1e7
        x = np.linspace(-scale, scale, shape[1])
        y = np.linspace(-scale, scale, shape[0])

        x2d, y2d = np.meshgrid(x, y)
        u = 10 * np.cos(2 * x2d / scale + 3 * y2d / scale)
        v = 20 * np.cos(6 * x2d / scale)

        return x, y, u, v, crs


    def main():
        fig = plt.figure(figsize=(8, 10))

        x, y, u, v, vector_crs = sample_data(shape=(50, 50))
        ax1 = fig.add_subplot(2, 1, 1, projection=ccrs.PlateCarree())
        ax1.coastlines('50m')
        ax1.set_extent([-45, 55, 20, 80], ccrs.PlateCarree())
        ax1.quiver(x, y, u, v, transform=vector_crs)

        ax2 = fig.add_subplot(2, 1, 2, projection=ccrs.PlateCarree())
        ax2.set_title('The same vector field regridded')
        ax2.coastlines('50m')
        ax2.set_extent([-45, 55, 20, 80], ccrs.PlateCarree())
        ax2.quiver(x, y, u, v, transform=vector_crs, regrid_shape=20)

        plt.show()


    if __name__ == '__main__':
        main()

**Total running time of the script:** ( 0 minutes  0.092 seconds)


.. _sphx_glr_download_gallery_regridding_arrows.py:


.. only :: html

 .. container:: sphx-glr-footer
    :class: sphx-glr-footer-example



  .. container:: sphx-glr-download

     :download:`Download Python source code: regridding_arrows.py <regridding_arrows.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: regridding_arrows.ipynb <regridding_arrows.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.readthedocs.io>`_