===================
GeoDjango Forms API
===================

.. module:: django.contrib.gis.forms
    :synopsis: GeoDjango forms API.

GeoDjango provides some specialized form fields and widgets in order to
visually display and edit geolocalized data on a map. By default, they use
`OpenLayers`_-powered maps, with a base WMS layer provided by `NASA`_.

.. _OpenLayers: https://openlayers.org/
.. _NASA: https://www.earthdata.nasa.gov/

Field arguments
===============
In addition to the regular :ref:`form field arguments <core-field-arguments>`,
GeoDjango form fields take the following optional arguments.

``srid``
--------

.. attribute:: Field.srid

    This is the SRID code that the field value should be transformed to. For
    example, if the map widget SRID is different from the SRID more generally
    used by your application or database, the field will automatically convert
    input values into that SRID.

``geom_type``
-------------

.. attribute:: Field.geom_type

    You generally shouldn't have to set or change that attribute which should
    be set up depending on the field class. It matches the OpenGIS standard
    geometry name.

``max_geom_collections``
------------------------

.. attribute:: Field.max_geom_collections

    .. versionadded:: 5.2.17

    The maximum number of geometry collections the field accepts before
    refusing to parse the input and raising a
    :exc:`~django.core.exceptions.ValidationError`. This guards against crashes
    in the underlying GEOS library when parsing deeply nested
    ``GEOMETRYCOLLECTION`` input. It defaults to ``198``.

    The limit is applied differently depending on the input format: for
    well-known text (WKT) it bounds the nesting *depth*, while for well-known
    binary (WKB and hex-encoded WKB) it bounds the *total* number of geometry
    collections (both breadth and depth). As a result, the same value may
    accept a wide, shallow collection as WKT but reject it as WKB. For GeoJSON,
    the limit is not applied at all, since GDAL parses that input type instead.

    Increase this value (or set to ``None``) only if you must accept
    legitimately deep geometries, since doing so reduces protection against
    fatal errors.

Form field classes
==================

``GeometryField``
-----------------

.. class:: GeometryField

``PointField``
--------------

.. class:: PointField

``LineStringField``
-------------------

.. class:: LineStringField

``PolygonField``
----------------

.. class:: PolygonField

``MultiPointField``
-------------------

.. class:: MultiPointField

``MultiLineStringField``
------------------------

.. class:: MultiLineStringField

``MultiPolygonField``
---------------------

.. class:: MultiPolygonField

``GeometryCollectionField``
---------------------------

.. class:: GeometryCollectionField

Form widgets
============

.. module:: django.contrib.gis.forms.widgets
    :synopsis: GeoDjango widgets API.

GeoDjango form widgets allow you to display and edit geographic data on a
visual map.
Note that none of the currently available widgets supports 3D geometries, hence
geometry fields will fallback using a ``Textarea`` widget for such data.

Widget attributes
-----------------

GeoDjango widgets are template-based, so their attributes are mostly different
from other Django widget attributes.

.. attribute:: BaseGeometryWidget.base_layer

    .. versionadded:: 6.0

    A string that specifies the identifier for the default base map layer to be
    used by the corresponding JavaScript map widget. It is passed as part of
    the widget options when rendering, allowing the ``MapWidget`` to determine
    which map tile provider or base layer to initialize (default is ``None``).

.. attribute:: BaseGeometryWidget.geom_type

    The OpenGIS geometry type, generally set by the form field.

.. attribute:: BaseGeometryWidget.map_srid

    SRID code used by the map (default is 4326).

.. attribute:: BaseGeometryWidget.display_raw

    Boolean value specifying if a textarea input showing the serialized
    representation of the current geometry is visible, mainly for debugging
    purposes (default is ``False``).

.. attribute:: BaseGeometryWidget.supports_3d

    Indicates if the widget supports edition of 3D data (default is ``False``).

.. attribute:: BaseGeometryWidget.template_name

    The template used to render the map widget.

You can pass widget attributes in the same manner that for any other Django
widget. For example::

    from django.contrib.gis import forms


    class MyGeoForm(forms.Form):
        point = forms.PointField(widget=forms.OSMWidget(attrs={"display_raw": True}))

Widget classes
--------------

``BaseGeometryWidget``

.. class:: BaseGeometryWidget

    This is an abstract base widget containing the logic needed by subclasses.
    You cannot directly use this widget for a geometry field.
    Note that the rendering of GeoDjango widgets is based on a base layer name,
    identified by the :attr:`base_layer` class attribute.

``OpenLayersWidget``

.. class:: OpenLayersWidget

    This is the default widget used by all GeoDjango form fields. Attributes
    are:

    .. attribute:: base_layer

        .. versionadded:: 6.0

        ``nasaWorldview``

    .. attribute:: template_name

        ``gis/openlayers.html``.

    .. attribute:: map_srid

        ``3857``

    ``OpenLayersWidget`` and :class:`OSMWidget` include the ``ol.js`` and
    ``ol.css`` files hosted on the ``cdn.jsdelivr.net`` content-delivery
    network. These files can be overridden by subclassing the widget and
    setting the ``js`` and ``css`` properties of the inner ``Media`` class (see
    :ref:`assets-as-a-static-definition`).

    .. admonition:: External assets with CSP

        When :class:`~django.middleware.csp.ContentSecurityPolicyMiddleware` is
        enabled, the default OpenLayers CDN assets (``ol.js`` and ``ol.css``)
        will be blocked unless explicitly allowed. This can be addressed in one
        of two ways: **serve assets locally** by subclassing the widget and
        provide local copies of the JavaScript and CSS files, or
        **allow the CDN in the CSP policy**.

        For example, to allow the default NASA Worldview base layer (replace
        ``x.y.z`` with the actual version)::

            from django.utils.csp import CSP

            SECURE_CSP = {
                "default-src": [CSP.SELF],
                "script-src": [CSP.SELF, "https://cdn.jsdelivr.net/npm/ol@x.y.z/dist/ol.js"],
                "style-src": [CSP.SELF, "https://cdn.jsdelivr.net/npm/ol@x.y.z/ol.css"],
                "img-src": [CSP.SELF, "https://*.earthdata.nasa.gov"],
            }

``OSMWidget``

.. class:: OSMWidget

    This widget specialized :class:`OpenLayersWidget` and uses an OpenStreetMap
    base layer to display geographic objects on. Attributes are:

    .. attribute:: base_layer

        .. versionadded:: 6.0

        ``osm``

    .. attribute:: default_lat
    .. attribute:: default_lon

        The default center latitude and longitude are ``47`` and ``5``,
        respectively, which is a location in eastern France.

    .. attribute:: default_zoom

        The default map zoom is ``12``.

    The :class:`OpenLayersWidget` note about using external assets also applies
    here. See also this `FAQ answer`_ about ``https`` access to map tiles.

    .. admonition:: OpenStreetMap tiles with CSP

        This widget uses OpenStreetMap tiles instead of NASA Worldview. If
        :ref:`security-csp` enabled, both the OpenLayers CDN resources (as
        required by :class:`OpenLayersWidget`) and the OpenStreetMap tile
        servers must be allowed::

            from django.utils.csp import CSP

            SECURE_CSP = {
                # other directives
                "img-src": [CSP.SELF, "https://tile.openstreetmap.org"],
            }

    .. _FAQ answer: https://help.openstreetmap.org/questions/10920/how-to-embed-a-map-in-my-https-site

    .. versionchanged:: 6.0

        The ``OSMWidget`` no longer uses a custom template. Consequently, the
        ``gis/openlayers-osm.html`` template was removed.

.. _geometry-widgets-customization:

Customizing the base layer used in OpenLayers-based widgets
-----------------------------------------------------------

.. versionadded:: 6.0

To customize the base layer displayed in OpenLayers-based geometry widgets,
define a new layer builder in a custom JavaScript file. For example:

.. code-block:: javascript
   :caption: ``path-to-file.js``

    MapWidget.layerBuilder.custom_layer_name = function () {
        // Return an OpenLayers layer instance.
        return new ol.layer.Tile({source: new ol.source.<ChosenSource>()});
    };

Then, subclass a standard geometry widget and set the ``base_layer``::

    from django.contrib.gis.forms.widgets import OpenLayersWidget


    class YourCustomWidget(OpenLayersWidget):
        base_layer = "custom_layer_name"

        class Media:
            js = ["path-to-file.js"]
