Merge pull request #1231 from rouault/fix_1229

proj_create_crs_to_crs(): defer selection of actual coordinate operation until proj_trans() is called (fixes #1229)

2 files changed, 14 insertions, 1 deletions

diff --git a/docs/source/apps/cs2cs.rst b/docs/source/apps/cs2cs.rst
index 8df67d72..579dc65e 100644
--- a/docs/source/apps/cs2cs.rst
+++ b/docs/source/apps/cs2cs.rst
@@ -154,6 +154,10 @@ When using a WKT definition or a AUTHORITY:CODE, the axis order of the CRS will
 be enforced. So for example if using EPSG:4326, the first value expected (or
 returned) will be a latitude.
 
+Internally, :program:`cs2cs` uses the :c:func:`proj_create_crs_to_crs` function
+to compute the appropriate coordinate operation, so implementation details of
+this function directly impact the results returned by the program.
+
 The environment parameter :envvar:`PROJ_LIB` establishes the
 directory for resource files (database, datum shift grids, etc.)
 
@@ -195,7 +199,7 @@ The x-y output data will appear as three lines of:
 
 ::
 
-    1402285.98  5076292.42 -0.00
+    1402293.44  5076292.68 0.00
 
 
 Using EPSG codes
diff --git a/docs/source/development/reference/functions.rst b/docs/source/development/reference/functions.rst
index 87271117..4052ff82 100644
--- a/docs/source/development/reference/functions.rst
+++ b/docs/source/development/reference/functions.rst
@@ -108,11 +108,20 @@ paragraph for more details.
           When using that syntax, the axis order and unit for geographic CRS will
           be longitude, latitude, and the unit degrees.
 
+        - the name of a CRS as found in the PROJ database, e.g "WGS84", "NAD27", etc.
+
         - more generally any string accepted by :c:func:`proj_create`
 
     An "area of use" can be specified in area. When it is supplied, the more
     accurate transformation between two given systems can be chosen.
 
+    When no area of use is specific and several coordinate operations are possible
+    depending on the area of use, this function will internally store those
+    candidate coordinate operations in the return PJ object. Each subsequent
+    coordinate transformation done with :c:func:`proj_trans` will then select
+    the appropriate coordinate operation by comparing the input coordinates with
+    the area of use of the candidate coordinate operations.
+
     Example call:
 
     .. code-block:: C