Add a new Vertical CRS section to the QGIS plugin project properties dialog, allowing users to select a vertical CRS for the mobile app to use when reporting elevation.

Behaviour

• By default, the section is disabled and no vertical CRS is set.
• When the checkbox is ticked, the dropdown can be used to select a specific vertical CRS. This is the common QGIS button to select CRS. It should filter out only vertical ones.
• If the selected CRS requires a geoid grid that is not present, show a warning with an option to download it automatically.
• If multiple transformations are available from EPSG:4979 to the selected CRS, show a warning prompting the user to select a specific one in the Transformations tab.
• The selection is written into project file using the following keys:
  • ElevationTransformationEnabled - the value of the checkbox
  • TargetVerticalCRS - selected CRS in WKT form

Resources

• Design: https://app.excalidraw.com/s/3CzSPAgBMbC/3Tp4itXs7vl?element=NgdkmcKT0PLGB-Kaeadyb

Acceptance criteria:

• Users can select vertical CRS in a new entry under project settings -> Mergin Maps tab
• The mobile app reacts to the settings and reports elevation transformed to the set vCRS.
• The plugin shows an error if a grid file is missing and offers an option to download it. This is available in the project settings and also in the validations tab (when syncing)
• The plugin informs user if a needed grid is found, available and properly packaged with a tick mark (✓).
• When there is more than one transformation between EPSG:4979 to the selected vertical CRS that require a grid file, the plugin suggests to choose a specific transformation in the "Transformations" tab.

  • This can be tested, for example, on EPSG:8357 (baltic heights) where the first transformation is for CZ and the second one for SK.