#138 WIP Validity

* adds geometry validity checks for SimpleGeomForm is_valid()
    * shows validity problems on the form if a feature is invalid
* optimizes merging of different features into one MultiPolygon
* further enhances tests
* adds as_feature_collection() method on Geometry model for converting geom MultiPolygon attribute into FeatureCollection json holding each polygon as an own feature -> makes each polygon selectable in new netgis map client

konova/models/geometry.py

@@ -5,11 +5,15 @@ Contact: michel.peltriaux@sgdnord.rlp.de
 Created on: 15.11.21
 
 """
+import json
+
 from django.contrib.gis.db.models import MultiPolygonField
+from django.contrib.gis.geos import Polygon
 from django.db import models, transaction
 from django.utils import timezone
 
 from konova.models import BaseResource, UuidModel
+from konova.sub_settings.lanis_settings import DEFAULT_SRID_RLP
 from konova.utils.wfs.spatial import ParcelWFSFetcher
 
 
@@ -179,6 +183,34 @@ class Geometry(BaseResource):
 
         return parcels
 
+    def as_feature_collection(self, srid=DEFAULT_SRID_RLP):
+        """ Returns a FeatureCollection structure holding all polygons of the MultiPolygon as single features
+
+        This method is used to convert a single MultiPolygon into multiple Polygons, which can be used as separated
+        features in the NETGIS map client.
+
+        Args:
+            srid (int): The spatial reference system identifier to be transformed to
+
+        Returns:
+            geojson (dict): The FeatureCollection json (as dict)
+        """
+        geom = self.geom
+        geom.transform(ct=srid)
+
+        polygons = []
+        for coords in geom.coords:
+            p = Polygon(coords[0], srid=geom.srid)
+            polygons.append(p)
+        geojson = {
+            "type": "FeatureCollection",
+            "features": [
+                json.loads(x.geojson) for x in polygons
+            ]
+        }
+        return geojson
+
+
 
 class GeometryConflict(UuidModel):
     """