.. _sphx_glr_gallery_eccentric_ellipse.py:


Displaying data on an eccentric ellipse
---------------------------------------

This example demonstrates plotting data on an eccentric ellipse. The data
plotted is a topography map of the asteroid Vesta. The map is actually an
image, which is defined on an equirectangluar projection relative to an
ellipse with a semi-major axis of 285 km and a semi-minor axis of 229 km.
The image is reprojected on-the-fly onto a geostationary projection with
matching eccentricity.





.. image:: /gallery/images/sphx_glr_eccentric_ellipse_001.png
    :align: center





.. code-block:: python

    try:
        from urllib2 import urlopen
    except ImportError:
        from urllib.request import urlopen
    from io import BytesIO

    import cartopy.crs as ccrs
    import matplotlib.pyplot as plt
    import numpy as np
    from PIL import Image


    def vesta_image():
        """
        Return an image of Vesta's topography.

        Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

        Returns
        -------
        img : numpy array
            The pixels of the image in a numpy array.
        img_proj : cartopy CRS
            The rectangular coordinate system of the image.
        img_extent : tuple of floats
            The extent of the image ``(x0, y0, x1, y1)`` referenced in
            the ``img_proj`` coordinate system.

        """
        url = 'https://www.nasa.gov/sites/default/files/pia17037.jpg'
        img_handle = BytesIO(urlopen(url).read())
        raw_image = Image.open(img_handle)
        # The image is extremely high-resolution, which takes a long time to
        # plot. Sub-sampling reduces the time taken to plot while not
        # significantly altering the integrity of the result.
        smaller_image = raw_image.resize([raw_image.size[0] // 10,
                                          raw_image.size[1] // 10])
        img = np.asarray(smaller_image)
        # We define the semimajor and semiminor axes, but must also tell the
        # globe not to use the WGS84 ellipse, which is its default behaviour.
        img_globe = ccrs.Globe(semimajor_axis=285000., semiminor_axis=229000.,
                               ellipse=None)
        img_proj = ccrs.PlateCarree(globe=img_globe)
        img_extent = (-895353.906273091, 895353.906273091,
                      447676.9531365455, -447676.9531365455)
        return img, img_globe, img_proj, img_extent


    def main():
        img, globe, crs, extent = vesta_image()
        projection = ccrs.Geostationary(globe=globe)

        fig = plt.figure()
        ax = fig.add_subplot(1, 1, 1, projection=projection)
        ax.imshow(img, transform=crs, extent=extent)
        fig.text(.075, .012, "Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI",
                 bbox={'facecolor': 'w', 'edgecolor': 'k'})
        plt.show()


    if __name__ == '__main__':
        main()

**Total running time of the script:** ( 0 minutes  38.010 seconds)



.. container:: sphx-glr-footer


  .. container:: sphx-glr-download

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



  .. container:: sphx-glr-download

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

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

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