Network: automatically use CDN resources when local resources not available, and networking enabled

4 files changed, 29 insertions, 3 deletions

diff --git a/docs/source/apps/cs2cs.rst b/docs/source/apps/cs2cs.rst
index d7f0e9ad..a4069472 100644
--- a/docs/source/apps/cs2cs.rst
+++ b/docs/source/apps/cs2cs.rst
@@ -175,6 +175,14 @@ normally be in DMS format (use ``-f %.12f`` for decimal degrees with 12 decimal
 places), while projected (cartesian) coordinates will be in linear
 (meter, feet) units.
 
+Use of remote grids
+-------------------
+
+.. versionadded:: 7.0.0
+
+If the :envvar:`PROJ_NETWORK` environment variable is set to ``ON``,
+:program:`cs2cs` will attempt to use remote grids stored on CDN (Content
+Delivery Network) storage, when they are not available locally.
 
 Examples
 ********
diff --git a/docs/source/apps/projinfo.rst b/docs/source/apps/projinfo.rst
index 6236056d..a9b6aecc 100644
--- a/docs/source/apps/projinfo.rst
+++ b/docs/source/apps/projinfo.rst
@@ -20,7 +20,7 @@ Synopsis
     |    [[--area name_or_code] | [--bbox west_long,south_lat,east_long,north_lat]]
     |    [--spatial-test contains|intersects]
     |    [--crs-extent-use none|both|intersection|smallest]
-    |    [--grid-check none|discard_missing|sort] [--show-superseded]
+    |    [--grid-check none|discard_missing|sort|known_available] [--show-superseded]
     |    [--pivot-crs always|if_no_direct_transformation|never|{auth:code[,auth:code]*}]
     |    [--boundcrs-to-wgs84]
     |    [--main-db-path path] [--aux-db-path path]*
@@ -148,12 +148,13 @@ The following control parameters can appear in any order:
 
     .. note:: only used for coordinate operation computation
 
-.. option:: --grid-check none|discard_missing|sort
+.. option:: --grid-check none|discard_missing|sort|known_available
 
     Specify how the presence or absence of a horizontal or vertical shift grid
     required for a coordinate operation affects the results returned when
     researching coordinate operations between 2 CRS.
-    The default strategy is ``sort``: in that case, all candidate
+    The default strategy is ``sort`` (if :envvar:`PROJ_NETWORK` is not defined).
+    In that case, all candidate
     operations are returned, but the actual availability of the grids is used
     to determine the sorting order. That is, if a coordinate operation involves
     using a grid that is not available in the PROJ resource directories
@@ -163,6 +164,9 @@ The following control parameters can appear in any order:
     this returns the results as if all the grids where available.
     The ``discard_missing`` strategy discards results that involve grids not
     present in the PROJ resource directories.
+    The ``known_available`` strategy discards results that involve grids not
+    present in the PROJ resource directories and that are not known of the CDN.
+    This is the default strategy is :envvar:`PROJ_NETWORK` is set to ``ON``.
 
     .. note:: only used for coordinate operation computation
 
diff --git a/docs/source/resource_files.rst b/docs/source/resource_files.rst
index 13b9386d..69cf2f95 100644
--- a/docs/source/resource_files.rst
+++ b/docs/source/resource_files.rst
@@ -40,6 +40,11 @@ The following paths are checked in order:
   PROJ installation is not moved somewhere else.
 - The current directory
 
+When networking capabilities are enabled, either by API with the
+:c:func:`proj_context_set_enable_network` function or when the
+:envvar:`PROJ_NETWORK` environment variable is set to ``ON``, PROJ will
+attempt to use remote grids stored on CDN (Content Delivery Network) storage.
+
 .. _proj-db:
 
 proj.db
diff --git a/docs/source/usage/environmentvars.rst b/docs/source/usage/environmentvars.rst
index 457432a0..00058716 100644
--- a/docs/source/usage/environmentvars.rst
+++ b/docs/source/usage/environmentvars.rst
@@ -56,3 +56,12 @@ done by setting the variable with no content::
     Set the debug level of PROJ. The default debug level is zero, which results
     in no debug output when using PROJ. A number from 1-3, whit 3 being the most
     verbose setting.
+
+.. envvar:: PROJ_NETWORK
+
+    .. versionadded:: 7.0.0
+
+    If set to ON, enable the capability to use remote grids stored on CDN
+    (Content Delivery Network) storage, when grids are not available locally.
+    Alternatively, the :c:func:`proj_context_set_enable_network` function can
+    be used.