From 748c1a5d2fd2d2d325b2784f85acd74e84d7762e Mon Sep 17 00:00:00 2001
From: DelazJ <delazj@gmail.com>
Date: Fri, 14 Feb 2025 12:15:23 +0100
Subject: [PATCH] Add expression functions to create CRS from string definition
 and to get CRS authid

Fixes #9641
---
 .../expressions/expression_help/CRS.rst       | 49 +++++++++++++++++++
 .../expression_help/GeometryGroup.rst         |  6 +--
 .../expressions/functions_list.rst            | 14 ++++++
 3 files changed, 66 insertions(+), 3 deletions(-)
 create mode 100644 docs/user_manual/expressions/expression_help/CRS.rst

diff --git a/docs/user_manual/expressions/expression_help/CRS.rst b/docs/user_manual/expressions/expression_help/CRS.rst
new file mode 100644
index 00000000000..f24c9bf1f16
--- /dev/null
+++ b/docs/user_manual/expressions/expression_help/CRS.rst
@@ -0,0 +1,49 @@
+:orphan:
+
+.. DO NOT EDIT THIS FILE DIRECTLY. It is generated automatically by
+   populate_expressions_list.py in the scripts folder.
+   Changes should be made in the function help files
+   in the resources/function_help/json/ folder in the
+   qgis/QGIS repository.
+
+.. _expression_function_CRS_crs_from_text:
+
+crs_from_text
+.............
+
+Creates a coordinate reference system from a string definition. The string can represent an auth:id code, a WKT definition, or a PROJ string definition of the CRS.
+
+.. list-table::
+   :widths: 15 85
+
+   * - Syntax
+     - crs_from_text(definition)
+   * - Arguments
+     - * **definition** - CRS definition
+   * - Examples
+     - * ``crs_from_text('EPSG:3857')`` → crs value 'EPSG:3857 - WGS 84 / Pseudo-Mercator'
+       * ``crs_from_text('PROJ:+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs +type=crs')`` → crs value 'EPSG:3857 - WGS 84 / Pseudo-Mercator'
+
+
+.. end_crs_from_text_section
+
+.. _expression_function_CRS_crs_to_authid:
+
+crs_to_authid
+.............
+
+Returns the authority:id identifier string for a coordinate reference system.
+
+.. list-table::
+   :widths: 15 85
+
+   * - Syntax
+     - crs_to_authid(crs)
+   * - Arguments
+     - * **crs** - crs value
+   * - Examples
+     - * ``crs_to_authid(crs_from_text('PROJ:+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs +type=crs'))`` → 'EPSG:3857'
+
+
+.. end_crs_to_authid_section
+
diff --git a/docs/user_manual/expressions/expression_help/GeometryGroup.rst b/docs/user_manual/expressions/expression_help/GeometryGroup.rst
index 1d8261aed9d..a1ec31326b7 100644
--- a/docs/user_manual/expressions/expression_help/GeometryGroup.rst
+++ b/docs/user_manual/expressions/expression_help/GeometryGroup.rst
@@ -170,7 +170,7 @@ Returns the north-based bearing as the angle in radians measured clockwise on th
    * - Arguments
      - * **point_a** - point geometry
        * **point_b** - point geometry
-       * **source_crs** - an optional string representing the source CRS of the points. By default the current layer's CRS is used.
+       * **source_crs** - an optional string or CRS object representing the source CRS of the points. By default the current layer's CRS is used.
        * **ellipsoid** - an optional string representing the acronym or the authority:ID (eg 'EPSG:7030') of the ellipsoid on which the bearing should be measured. By default the current project's ellipsoid setting is used.
    * - Examples
      - * ``degrees( bearing( make_point(16198544, -4534850), make_point(18736872, -1877769), 'EPSG:3857', 'EPSG:7030') )`` → 49.980071
@@ -3198,8 +3198,8 @@ Returns the geometry transformed from a source CRS to a destination CRS.
      - transform(geometry, source_auth_id, dest_auth_id)
    * - Arguments
      - * **geometry** - a geometry
-       * **source_auth_id** - the source auth CRS ID
-       * **dest_auth_id** - the destination auth CRS ID
+       * **source_auth_id** - the source CRS definition or CRS object
+       * **dest_auth_id** - the destination CRS definition or CRS object
    * - Examples
      - * ``geom_to_wkt( transform( make_point(488995.53240249, 7104473.38600835), 'EPSG:2154', 'EPSG:4326' ) )`` → 'POINT(0 51)'
 
diff --git a/docs/user_manual/expressions/functions_list.rst b/docs/user_manual/expressions/functions_list.rst
index dd381161f4c..b5a853ea069 100644
--- a/docs/user_manual/expressions/functions_list.rst
+++ b/docs/user_manual/expressions/functions_list.rst
@@ -176,6 +176,20 @@ Further reading: :ref:`expression_function_Date_and_Time_format_date`
 .. include:: expression_help/Conversions.rst
    :start-after: .. end_to_time_section
 
+
+CRS Functions
+-----------------
+
+This group contains functions to operate on coordinate reference system objects.
+
+.. include:: text_include.rst
+   :start-after: .. functions_group_toc
+   :end-before: .. end_functions_group_toc
+
+.. include:: expression_help/CRS.rst
+   :start-after: :orphan:
+
+
 Custom Functions
 -----------------