Restructure coordinate operations docs

OSGeo · Nov 27, 2017 · 410ad2d · 410ad2d
1 parent 83fa46d
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Showing 9 changed files with 34 additions and 10 deletions.
diff --git a/...e/operations/transformations/axisswap.rst → ...usage/operations/conversions/axisswap.rst b/...e/operations/transformations/axisswap.rst → ...usage/operations/conversions/axisswap.rst
diff --git a/...usage/operations/transformations/cart.rst → ...rce/usage/operations/conversions/cart.rst b/...usage/operations/transformations/cart.rst → ...rce/usage/operations/conversions/cart.rst
diff --git a/docs/source/usage/operations/conversions/index.rst b/docs/source/usage/operations/conversions/index.rst
@@ -0,0 +1,18 @@
+.. _conversions_list:
+
+================================================================================
+Conversions
+================================================================================
+
+Conversions are coordinate operations in which both coordinate reference systems
+are based on the same datum. In PROJ.4 projections are differentiated from
+conversions.
+
+.. toctree::
+   :maxdepth: 1
+
+   axisswap
+   cart
+   lonlat
+   latlon
+   unitconvert
diff --git a/...e/usage/operations/projections/latlon.rst → ...e/usage/operations/conversions/latlon.rst b/...e/usage/operations/projections/latlon.rst → ...e/usage/operations/conversions/latlon.rst
diff --git a/...e/usage/operations/projections/lonlat.rst → ...e/usage/operations/conversions/lonlat.rst b/...e/usage/operations/projections/lonlat.rst → ...e/usage/operations/conversions/lonlat.rst
diff --git a/...perations/transformations/unitconvert.rst → ...ge/operations/conversions/unitconvert.rst b/...perations/transformations/unitconvert.rst → ...ge/operations/conversions/unitconvert.rst
diff --git a/docs/source/usage/operations/index.rst b/docs/source/usage/operations/index.rst
@@ -4,15 +4,18 @@
 Coordinate operations
 ================================================================================
 
-Coordinate operations in PROJ.4 are divided into two groups:
-Projections and transformations.
-Projections are purely cartographic mappings of the sphere onto the plane whereas
-transformations are mostly geodetic operations concerned with changes in
-reference frames.
+Coordinate operations in PROJ.4 are divided into three groups:
+Projections, conversions  and transformations.
+Projections are purely cartographic mappings of the sphere onto the plane.
+Technically projections are conversions (according to ISO standards), though in
+PROJ.4 projections are distinguished from conversions. Conversions are coordinate
+operations that do not exert a change in reference frame. Operations that do
+exert a change in reference frame are called transformations.
 
 .. toctree::
    :maxdepth: 1
 
    projections/index
+   conversions/index
    transformations/index
 
diff --git a/docs/source/usage/operations/projections/index.rst b/docs/source/usage/operations/projections/index.rst
@@ -4,6 +4,11 @@
 Projections
 ================================================================================
 
+Projections are coordinate operations that are technically conversions but since
+projections are so fundamental to PROJ.4 we differentiate them from conversions.
+
+Projections map the spherical 3D space to a flat 2D space.
+
 .. toctree::
    :maxdepth: 1
 
@@ -62,8 +67,6 @@ Projections
    lagrng
    larr
    lask
-   lonlat
-   latlon
    lcc
    lcca
    leac

diff --git a/docs/source/usage/operations/transformations/index.rst b/docs/source/usage/operations/transformations/index.rst
@@ -4,13 +4,13 @@
 Transformations
 ================================================================================
 
+Transformations coordinate operation in which the two coordinate reference
+systems are based on different datums.
+
 .. toctree::
    :maxdepth: 1
 
-   axisswap
-   cart
    helmert
    molodensky
    hgridshift
    vgridshift
-   unitconvert