# Τεκμηρίωση του Django - 1.10.7

# Πηγαίος κώδικας για το django.contrib.gis.admin.options

    from django.contrib.admin import ModelAdmin
    from django.contrib.gis.admin.widgets import OpenLayersWidget
    from django.contrib.gis.db import models
    from django.contrib.gis.gdal import HAS_GDAL, OGRGeomType
    from django.core.exceptions import ImproperlyConfigured

    spherical_mercator_srid = 3857

    class GeoModelAdmin(ModelAdmin):
        """
        The administration options class for Geographic models. Map settings
        may be overloaded from their defaults to create custom maps.
        """
        # The default map settings that may be overloaded -- still subject
        # to API changes.
        default_lon = 0
        default_lat = 0
        default_zoom = 4
        display_wkt = False
        display_srid = False
        extra_js = []
        num_zoom = 18
        max_zoom = False
        min_zoom = False
        units = False
        max_resolution = False
        max_extent = False
        modifiable = True
        mouse_position = True
        scale_text = True
        layerswitcher = True
        scrollable = True
        map_width = 600
        map_height = 400
        map_srid = 4326
        map_template = 'gis/admin/openlayers.html'
        openlayers_url = 'http://openlayers.org/api/2.13.1/OpenLayers.js'
        point_zoom = num_zoom - 6
        wms_url = 'http://vmap0.tiles.osgeo.org/wms/vmap0'
        wms_layer = 'basic'
        wms_name = 'OpenLayers WMS'
        wms_options = {'format': 'image/jpeg'}
        debug = False
        widget = OpenLayersWidget

        @property
        def media(self):
            "Injects OpenLayers JavaScript into the admin."
            media = super(GeoModelAdmin, self).media
            media.add_js([self.openlayers_url])
            media.add_js(self.extra_js)
            return media

        def formfield_for_dbfield(self, db_field, request, **kwargs):
            """
            Overloaded from ModelAdmin so that an OpenLayersWidget is used
            for viewing/editing 2D GeometryFields (OpenLayers 2 does not support
            3D editing).
            """
            if isinstance(db_field, models.GeometryField) and db_field.dim < 3:
                if not HAS_GDAL and db_field.srid != self.map_srid:
                    raise ImproperlyConfigured(
                        "Map SRID is %s and SRID of `%s` is %s. GDAL must be "
                        "installed to perform the transformation."
                        % (self.map_srid, db_field, db_field.srid)
                    )
                # Setting the widget with the newly defined widget.
                kwargs['widget'] = self.get_map_widget(db_field)
                return db_field.formfield(**kwargs)
            else:
                return super(GeoModelAdmin, self).formfield_for_dbfield(db_field, request, **kwargs)

        def get_map_widget(self, db_field):
            """
            Returns a subclass of the OpenLayersWidget (or whatever was specified
            in the `widget` attribute) using the settings from the attributes set
            in this class.
            """
            is_collection = db_field.geom_type in ('MULTIPOINT', 'MULTILINESTRING', 'MULTIPOLYGON', 'GEOMETRYCOLLECTION')
            if is_collection:
                if db_field.geom_type == 'GEOMETRYCOLLECTION':
                    collection_type = 'Any'
                else:
                    collection_type = OGRGeomType(db_field.geom_type.replace('MULTI', ''))
            else:
                collection_type = 'None'

            class OLMap(self.widget):
                template = self.map_template
                geom_type = db_field.geom_type

                wms_options = ''
                if self.wms_options:
                    wms_options = ["%s: '%s'" % pair for pair in self.wms_options.items()]
                    wms_options = ', %s' % ', '.join(wms_options)

                params = {'default_lon': self.default_lon,
                          'default_lat': self.default_lat,
                          'default_zoom': self.default_zoom,
                          'display_wkt': self.debug or self.display_wkt,
                          'geom_type': OGRGeomType(db_field.geom_type),
                          'field_name': db_field.name,
                          'is_collection': is_collection,
                          'scrollable': self.scrollable,
                          'layerswitcher': self.layerswitcher,
                          'collection_type': collection_type,
                          'is_generic': db_field.geom_type == 'GEOMETRY',
                          'is_linestring': db_field.geom_type in ('LINESTRING', 'MULTILINESTRING'),
                          'is_polygon': db_field.geom_type in ('POLYGON', 'MULTIPOLYGON'),
                          'is_point': db_field.geom_type in ('POINT', 'MULTIPOINT'),
                          'num_zoom': self.num_zoom,
                          'max_zoom': self.max_zoom,
                          'min_zoom': self.min_zoom,
                          'units': self.units,  # likely should get from object
                          'max_resolution': self.max_resolution,
                          'max_extent': self.max_extent,
                          'modifiable': self.modifiable,
                          'mouse_position': self.mouse_position,
                          'scale_text': self.scale_text,
                          'map_width': self.map_width,
                          'map_height': self.map_height,
                          'point_zoom': self.point_zoom,
                          'srid': self.map_srid,
                          'display_srid': self.display_srid,
                          'wms_url': self.wms_url,
                          'wms_layer': self.wms_layer,
                          'wms_name': self.wms_name,
                          'wms_options': wms_options,
                          'debug': self.debug,
                          }
            return OLMap

    class OSMGeoAdmin(GeoModelAdmin):
        map_template = 'gis/admin/osm.html'
        num_zoom = 20
        map_srid = spherical_mercator_srid
        max_extent = '-20037508,-20037508,20037508,20037508'
        max_resolution = '156543.0339'
        point_zoom = num_zoom - 6
        units = 'm'