Merge remote-tracking branch 'osgeo/master' into doc-improvements

7 files changed, 118 insertions, 6 deletions

diff --git a/docs/source/operations/conversions/unitconvert.rst b/docs/source/operations/conversions/unitconvert.rst
index 50ac832c..bc422afb 100644
--- a/docs/source/operations/conversions/unitconvert.rst
+++ b/docs/source/operations/conversions/unitconvert.rst
@@ -109,4 +109,6 @@ In the table below all time units supported by PROJ is listed.
 +--------------+-----------------------------+
 | gps_week     | GPS Week                    |
 +--------------+-----------------------------+
+| yyyymmdd     | Date in yyyymmdd format     |
++--------------+-----------------------------+
 
diff --git a/docs/source/operations/projections/aeqd.rst b/docs/source/operations/projections/aeqd.rst
index 32165e49..d4baa8b6 100644
--- a/docs/source/operations/projections/aeqd.rst
+++ b/docs/source/operations/projections/aeqd.rst
@@ -12,7 +12,10 @@ Azimuthal Equidistant
 +---------------------+----------------------------------------------------------+
 | **Options**                                                                    |
 +---------------------+----------------------------------------------------------+
-| `+guam`             |  Use Guam elliptical formulas. Defaults to false.        |
+| `+guam`             | Use Guam elliptical formulas. Only accurate near the     |
+|                     | Island of Guam (:math:`\lambda\approx 144.5^{\circ}`,    |
+|                     | :math:`\phi\approx 13.5^{\circ}`)                        |
+|                     | Defaults to false.                                       |
 +---------------------+----------------------------------------------------------+
 
 
diff --git a/docs/source/operations/projections/airy.rst b/docs/source/operations/projections/airy.rst
index d2730592..eefda4e9 100644
--- a/docs/source/operations/projections/airy.rst
+++ b/docs/source/operations/projections/airy.rst
@@ -3,6 +3,11 @@
 ********************************************************************************
 Airy
 ********************************************************************************
+
+The Airy projection is an azimuthal minimum error projection for the region
+within the small or great circle defined by an angular distance,
+:math:`\phi_b`, from the tangency point of the plane :math:`( \lambda_0, \phi_0 )`.
+
 +---------------------+----------------------------------------------------------+
 | **Classification**  |                                                          |
 +---------------------+----------------------------------------------------------+
@@ -14,7 +19,10 @@ Airy
 +---------------------+----------------------------------------------------------+
 | **Options**                                                                    |
 +---------------------+----------------------------------------------------------+
-| `+lat_b`            |                                                          |
+| `+lat_b`            | Angular distance from tangency point of the plane        |
+|                     | :math:`( \lambda_0, \phi_0 )` where the error is kept at |
+|                     | minimum. Defaults to :math:`90^{\circ}` which is         |
+|                     | suitable for hemispherical maps.                         |
 +---------------------+----------------------------------------------------------+
 | `+no_cut`           | Do not cut at hemisphere limit                           |
 +---------------------+----------------------------------------------------------+
diff --git a/docs/source/operations/projections/eqc.rst b/docs/source/operations/projections/eqc.rst
index be431977..5833bd61 100644
--- a/docs/source/operations/projections/eqc.rst
+++ b/docs/source/operations/projections/eqc.rst
@@ -64,9 +64,8 @@ Example using EPSG 32662 (WGS84 Plate Carrée)::
 
 Example using Plate Carrée projection with true scale at latitude 30° and central meridian 90°W::
 
-    $ echo -88 30 | proj +proj=eqc +lat_ts=30 +lat_0=90w
-    -8483684.61     13358338.90
-
+    $ echo -88 30 | proj +proj=eqc +lat_ts=30 +lon_0=90w
+    192811.01       3339584.72
 
 Mathematical definition
 #######################
diff --git a/docs/source/operations/projections/index.rst b/docs/source/operations/projections/index.rst
index 9255d9fd..77decd6c 100644
--- a/docs/source/operations/projections/index.rst
+++ b/docs/source/operations/projections/index.rst
@@ -141,6 +141,7 @@ Projections map the spherical 3D space to a flat 2D space.
    wag5
    wag6
    wag7
+   webmerc
    weren
    wink1
    wink2
diff --git a/docs/source/operations/projections/nsper.rst b/docs/source/operations/projections/nsper.rst
index 4a8651fc..d204305b 100644
--- a/docs/source/operations/projections/nsper.rst
+++ b/docs/source/operations/projections/nsper.rst
@@ -4,7 +4,28 @@
 Near-sided perspective
 ********************************************************************************
 
+The near-sided perspective projection simulates a view from a height
+:math:`h` similar to how a satellite in orbit would see it.
+
++---------------------+-------------------------------------------------------------+
+| **Classification**  | Azimuthal. Neither conformal nor equal area.                |
++---------------------+-------------------------------------------------------------+
+| **Available forms** | Forward and inverse spherical projection                    |
++---------------------+-------------------------------------------------------------+
+| **Defined area**    | Global, although for one hemisphere at a time.              |
++---------------------+-------------------------------------------------------------+
+| **Options**                                                                       |
++---------------------+-------------------------------------------------------------+
+| `+h`                | Height of the view point above the Earth and must be in     |
+|                     | the same units as the radius of the sphere. Required.       |
++---------------------+-------------------------------------------------------------+
+| `+lat_0`            | Latitude (in degrees) of the view position. Defaults to 0.  |
++---------------------+-------------------------------------------------------------+
+| `+lon_0`            | Longitude (in degrees) of the view position. Defaults to 0. |
++---------------------+-------------------------------------------------------------+
+
+
 .. image:: ./images/nsper.png
    :scale: 50%
-   :alt:   Near-sided perspective  
+   :alt:   Near-sided perspective
 
diff --git a/docs/source/operations/projections/webmerc.rst b/docs/source/operations/projections/webmerc.rst
new file mode 100644
index 00000000..0c465afc
--- /dev/null
+++ b/docs/source/operations/projections/webmerc.rst
@@ -0,0 +1,78 @@
+.. _webmerc:
+
+********************************************************************************
+Web Mercator / Pseudo Mercator
+********************************************************************************
+
+The Web Mercator / Pseudo Mercator projection is a cylindrical map projection.
+This is a variant of the regular :ref:`merc` projection, except that the computation
+is done on a sphere, using the semi-major axis of the ellipsoid.
+
+From `Wikipedia <https://en.wikipedia.org/wiki/Web_Mercator>`_:
+
+    This projection is widely used by the Web Mercator, Google Web Mercator,
+    Spherical Mercator, WGS 84 Web Mercator[1] or WGS 84/Pseudo-Mercator is a
+    variant of the Mercator projection and is the de facto standard for Web
+    mapping applications. [...]
+    It is used by virtually all major online map providers [...]
+    Its official EPSG identifier is EPSG:3857, although others have been used
+    historically.
+
+
++---------------------+----------------------------------------------------------+
+| **Classification**  | Cylindrical (non conformant if used with ellipsoid)      |
++---------------------+----------------------------------------------------------+
+| **Version**         | Added in proj 5.1.0                                      |
++---------------------+----------------------------------------------------------+
+| **Available forms** | Forward and inverse, spherical projection                |
++---------------------+----------------------------------------------------------+
+| **Defined area**    | Global, but best used near the equator                   |
++---------------------+----------------------------------------------------------+
+| **Options**         | Neither lat_0, lon_0, lat_ts or k_0 should be used.      |
++---------------------+----------------------------------------------------------+
+
+Usage
+########
+
+Example::
+
+    $ echo 2 49 | proj +proj=webmerc +datum=WGS84
+    222638.98       6274861.39
+
+Mathematical definition
+#######################
+
+The formulas describing the Mercator projection are all taken from G. Evenden's libproj manuals [Evenden2005]_.
+
+Forward projection
+==================
+
+.. math::
+
+    x = \lambda
+
+.. math::
+
+    y = \ln \left[ \tan \left(\frac{\pi}{4} + \frac{\phi}{2} \right) \right]
+
+
+Inverse projection
+==================
+
+.. math::
+
+    \lambda = {x}
+
+.. math::
+
+    \phi = \frac{\pi}{2} - 2 \arctan \left[ e^{-y} \right]
+
+
+
+Further reading
+###############
+
+#. `Wikipedia <https://en.wikipedia.org/wiki/Web_Mercator>`_
+
+
+