Docs: Add new Ellipsoids page to explain ellipsoidal parameters (#2922)

Co-authored-by: Rohit <rohitpingale103@gmail.com> Co-authored-by: Brendan Jurd <brendan.jurd@geoplex.com.au> Co-authored-by: Mike Taves <mwtoews@gmail.com>
OSGeo · Nov 20, 2021 · f932502 · f932502
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diff --git a/docs/images/general_ellipsoid.png b/docs/images/general_ellipsoid.png
diff --git a/docs/images/general_ellipsoid.svg b/docs/images/general_ellipsoid.svg
diff --git a/docs/source/operations/options/R.rst b/docs/source/operations/options/R.rst
@@ -1,4 +1,6 @@
 .. option:: +R=<value>
 
-    Radius of the sphere given in meters. If used in conjunction with ``+ellps``,
-    ``+R`` takes precedence.
+    Radius of the sphere, given in meters. If used in conjunction with
+    ``+ellps``, :option:`+R` takes precedence.
+
+    See :ref:`ellipsoid_size_parameters` for more information.
diff --git a/docs/source/operations/options/ellps.rst b/docs/source/operations/options/ellps.rst
@@ -1,5 +1,8 @@
 .. option:: +ellps=<value>
 
-    See :option:`proj -le` for a list of available ellipsoids.
+    The name of a built-in ellipsoid definition.
+
+    See :ref:`ellipsoids` for more information, or execute
+    :option:`proj -le` for a list of built-in ellipsoid names.
 
     *Defaults to "GRS80".*