.. _eck4:

********************************************************************************
Eckert IV
********************************************************************************

+---------------------+----------------------------------------------------------+
| **Classification**  | Pseudocylindrical                                        |
+---------------------+----------------------------------------------------------+
| **Available forms** | Forward and inverse, spherical projection                |
+---------------------+----------------------------------------------------------+
| **Defined area**    | Global                                                   |
+---------------------+----------------------------------------------------------+
| **Alias**           | eck4                                                     |
+---------------------+----------------------------------------------------------+
| **Domain**          | 2D                                                       |
+---------------------+----------------------------------------------------------+
| **Input type**      | Geodetic coordinates                                     |
+---------------------+----------------------------------------------------------+
| **Output type**     | Projected coordinates                                    |
+---------------------+----------------------------------------------------------+


.. figure:: ./images/eck4.png
   :width: 500 px
   :align: center
   :alt:   Eckert IV

   proj-string: ``+proj=eck4``

.. math::

    x = \lambda(1+cos\phi) / \sqrt{ 2 + \pi }

.. math::
    y = 2 \phi / \sqrt { 2 + \pi }

Parameters
################################################################################

.. note:: All parameters are optional for the Eckert IV projection.

.. include:: ../options/lon_0.rst

.. include:: ../options/R.rst

.. include:: ../options/x_0.rst

.. include:: ../options/y_0.rst