Support for more generic Space Oblique Mercator (SOM) projection

docs/plot/plotdefs.json

@@ -1321,6 +1321,18 @@
         "res": "med",
         "type": "poly"
     },
+    {
+        "filename": "som.png",
+        "latmax": 90,
+        "latmin": -90,
+        "lonmax": 180,
+        "lonmin": -180,
+        "name": "som",
+        "projstring": "+proj=som +inc_angle=98.303820000243860022 +ps_rev=0.06866666666666667 +asc_lon=64.412896137498847793",
+        "res": "low",
+        "type": "line",
+        "delta_cut": 1e7
+    },
     {
         "filename": "stere.png",
         "latmax": 90.0,

docs/source/operations/projections/index.rst

@@ -131,6 +131,7 @@ Projections map the spherical 3D space to a flat 2D space.
    s2
    sch
    sinu
+   som
    somerc
    stere
    sterea

docs/source/operations/projections/lsat.rst

@@ -4,6 +4,14 @@
 Space oblique for LANDSAT
 ********************************************************************************
 
+Space oblique for LANDSAT is a specialization of :doc:`Space Oblique Mercator<som>`
+which specifies the appropriate ascending longitude, inclination angle, and 
+orbital period for Landsat satellites, based on their satellite designation / id
+and path number.
+
+"Paths" are the repeating ground tracks that are traced by sun-synchronous
+satellites like those of the Landsat program.
+
 +---------------------+----------------------------------------------------------+
 | **Classification**  | Cylindrical                                              |
 +---------------------+----------------------------------------------------------+
@@ -56,3 +64,10 @@ Optional
 .. include:: ../options/x_0.rst
 
 .. include:: ../options/y_0.rst
+
+Further reading
+###############
+
+#. `Landsat Wikipedia <https://en.wikipedia.org/wiki/Landsat_program>`_
+#. :doc:`Space Oblique Mercator Projection<som>`
+

docs/source/operations/projections/misrsom.rst

@@ -4,6 +4,15 @@
 Space oblique for MISR
 ********************************************************************************
 
+Space oblique for MISR is a specialization of :doc:`Space Oblique Mercator<som>`
+which specifies the appropriate ascending longitude, inclination angle, and orbital
+period for Multi-angle Imaging Spectroradiometer (MISR) orbits, based on the path
+number for the orbit.
+
+"Paths" are the repeating ground tracks that are traced by sun-synchronous
+satellites like Terra on which the MISR instrument is aboard.
+
+
 +---------------------+----------------------------------------------------------+
 | **Classification**  | Conformal                                                |
 +---------------------+----------------------------------------------------------+
@@ -51,3 +60,8 @@ Optional
 .. include:: ../options/x_0.rst
 
 .. include:: ../options/y_0.rst
+
+#. `MISR Wikipedia <https://en.wikipedia.org/wiki/Landsat_program>`_
+#. `Terra Wikipedia <https://en.wikipedia.org/wiki/Terra_(satellite)>`_
+#. :doc:`Space Oblique Mercator Projection<som>`
+

docs/source/operations/projections/som.rst

@@ -0,0 +1,88 @@
+.. _som:
+
+********************************************************************************
+Space Oblique Mercator (SOM)
+********************************************************************************
+
+The Space Oblique Mercator (SOM) projection is a generalization of the Oblique
+Mercator projection, itself an (oblique) aspect of the Mercator projection with
+origins in the 16th century. In the previously available map projections, ground
+tracks of satellites traced curved lines which complicated their use in
+representing satellite remote sensing data. In response, SOM was specifically
+designed to represent satellite ground tracks as straight lines. This had the
+effect of minimizing distortions of data along a ground track and allowing
+satellite data to be represented accurately as a rectangular array.
+
+
+
++---------------------+----------------------------------------------------------+
+| **Classification**  | Conformal                                                |
++---------------------+----------------------------------------------------------+
+| **Available forms** | Forward and inverse, spherical and ellipsoidal           |
++---------------------+----------------------------------------------------------+
+| **Defined area**    | Global                                                   |
++---------------------+----------------------------------------------------------+
+| **Alias**           | som                                                      |
++---------------------+----------------------------------------------------------+
+| **Domain**          | 2D                                                       |
++---------------------+----------------------------------------------------------+
+| **Input type**      | Geodetic coordinates                                     |
++---------------------+----------------------------------------------------------+
+| **Output type**     | Projected coordinates                                    |
++---------------------+----------------------------------------------------------+
+
+
+.. figure:: ./images/som.png
+   :width: 500 px
+   :align: center
+   :alt:   Space Oblique Mercator (SOM)
+
+
+   proj-string: ``+proj=som +inc_angle=98.303820000243860022 +ps_rev=0.06866666666666667 +asc_lon=64.412896137498847793``
+
+   proj-string: ``+proj=som +inc_angle=1.7157253262878522r +ps_rev=0.06866666666666667 +asc_lon=1.1242171183417042r``
+
+Parameters
+################################################################################
+
+Required
+--------------------------------------------------------------------------------
+
+.. option:: +asc_lon=<value>
+
+    Longitude of the ascending node for the orbit (decimal degrees).
+
+.. option:: +inc_angle=<value>
+
+    Inclination (vertical tilt) of the orbit with respect to the reference plane, measured at the ascending node (decimal degrees).
+
+.. option:: +ps_rev=<value>
+
+    Time required for a single orbit (days).
+
+.. note::
+
+    To specify asc_lon or inc_angle in radians (instead of degrees). Follow the value with the "r" character.
+
+    As an example, to specify the ascending longitude as 1.1242171183417042 radians (~64.4129 decimal degrees): `+asc_lon=1.1242171183417042r`.
+
+   For more information see :doc:`projections usage<../../usage/projections>`.
+
+Optional
+--------------------------------------------------------------------------------
+
+.. include:: ../options/lon_0.rst
+
+.. include:: ../options/ellps.rst
+
+.. include:: ../options/R.rst
+
+.. include:: ../options/x_0.rst
+
+.. include:: ../options/y_0.rst
+
+Further reading
+###############
+
+#. `Space Oblique Mercator Wikipedia <https://en.wikipedia.org/wiki/Space-oblique_Mercator_projection>`_
+#. `USGS Report on Space Oblique Mercator Mathematical Development <https://web.archive.org/web/20211213011807/https://pubs.usgs.gov/bul/1518/report.pdf>`_

docs/source/spelling_wordlist.txt

@@ -123,6 +123,7 @@ ogc
 omerc
 OSGeo
 osgeo
+som
 srs
 tmerc
 towgs

src/lib_proj.cmake

@@ -67,8 +67,7 @@ set(SRC_LIBPROJ_PROJECTIONS
   projections/eqc.cpp
   projections/gall.cpp
   projections/labrd.cpp
-  projections/lsat.cpp
-  projections/misrsom.cpp
+  projections/som.cpp
   projections/merc.cpp
   projections/mill.cpp
   projections/ocea.cpp

src/pj_list.h

@@ -147,6 +147,7 @@ PROJ_HEAD(s2, "S2")
 PROJ_HEAD(sch, "Spherical Cross-track Height")
 PROJ_HEAD(set, "Set coordinate value")
 PROJ_HEAD(sinu, "Sinusoidal (Sanson-Flamsteed)")
+PROJ_HEAD(som, "Space Oblique Mercator")
 PROJ_HEAD(somerc, "Swiss. Obl. Mercator")
 PROJ_HEAD(stere, "Stereographic")
 PROJ_HEAD(sterea, "Oblique Stereographic Alternative")