Add MapExport chapter

Author: manisandro

qwc2.yml.in

@@ -13,6 +13,7 @@ nav:
             - Search: topics/Search.md
             - Feature info: topics/FeatureInfo.md
             - Printing: topics/Printing.md
+            - Map export: topics/MapExport.md
             - Map info: topics/Mapinfo.md
             - Editing: topics/Editing.md
             - Snapping: topics/Snapping.md

src/topics/MapExport.md

@@ -0,0 +1,59 @@
+# Map export
+
+The [MapExport](../references/qwc2_plugins.md#mapexport) plugin allows exporting a selected portion of the map to a variety of formats, as supported by the QGIS Server, among which:
+
+* Image formats (`image/png`, `image/jpeg`, `image/geotiff`, ...)
+* DXF (`application/dxf`)
+* GeoPDF (`application/pdf`)
+
+See the [MapExport plugin reference](../references/qwc2_plugins.md#mapexport) for a list of configuration options.
+
+In particular, the plugin supports specifying different export configurations for each format, i.e.:
+```
+      {
+        "name": "MapExport",
+        "cfg": {
+          "formatConfiguration": {
+            "application/dxf": [
+              {"name": "default"},
+              {
+                "name": "Geobau",
+                "extraQuery": "LAYERS=dxfgeobau",
+                "formatOptions": "MODE:NOSYMBOLOGY"
+              }
+            ],
+            "image/png": [
+              {"name": "default"},
+              {"name": "With baselayer", "baseLayer": "SWISSIMAGE"}
+            ]
+          }
+        }
+      },
+```
+
+For each format, if multiple configurations are defined, a combobox will be displayed to choose an export configuration.
+
+## Export to image formats
+For image formats, it may be desired to override the background layer for the exported map. To this end, specify a `baseLayer` in the format configuration to the name of a background `printLayer`.
+
+For GeoTIFF image export to become available, set up the `wms_geotiff_output` [QGIS Server plugin](https://github.com/qwc-services/qwc-qgis-server-plugins):
+
+```yml
+  qwc-qgis-server:
+    image: docker.io/sourcepole/qwc-qgis-server:<TAG>
+    volumes:
+      - ./volumes/qgis-server-plugins/wms_geotiff_output:/usr/share/qgis/python/plugins/wms_geotiff_output:ro
+    ...
+```
+
+# DXF export
+To enable the DXF export format, the desired layers are marked as *Published* in the QGIS Project Properties &to; QGIS Server &to; WFS/OAPIF.
+
+You can configure the DXF export by passing supported [`FORMAT_OPTIONS`](https://docs.qgis.org/latest/en/docs/server_manual/services.html#wms-formatoptions) as `formatOptions`, i.e.
+
+    "formatOptions": "MODE:NOSYMBOLOGY;NO_MTEXT:1"
+
+# GeoPDF export
+GeoPDF export is available since QGIS Server 3.36. As opposed generating a PDF via `GetPrint` (as used by the `Print`-Plugin), the MapExport plugin generates the GeoPDF via `GetMap` and will return just the selected export area as a GeoPDF, without relying on any print layout defined in the QGIS project.
+
+You can configure the GeoPDF export by passing supported `FORMAT_OPTIONS`, look for `PdfFormatOption` in [https://github.com/qgis/QGIS/blob/master/src/server/services/wms/qgswmsparameters.h](https://github.com/qgis/QGIS/blob/master/src/server/services/wms/qgswmsparameters.h).