Geometry simplification

* simplifies geometries on SimpleGeomForm if threshold GEOM_MAX_VERTICES has been exceeded
    * geometry is iteratively simplified to find a proper tolerance value which satisfies the GEOM_MAX_VERTICES threshold

konova/forms/geometry_form.py

@@ -15,6 +15,7 @@ from django.utils.translation import gettext_lazy as _
 
 from konova.forms.base_form import BaseForm
 from konova.models import Geometry
+from konova.settings import GEOM_MAX_VERTICES
 from konova.tasks import celery_update_parcels, celery_check_for_geometry_conflicts
 from konova.sub_settings.lanis_settings import DEFAULT_SRID_RLP
 from user.models import UserActionLogEntry
@@ -25,6 +26,7 @@ class SimpleGeomForm(BaseForm):
 
     """
     read_only = True
+    geometry_simplified = False
     geom = MultiPolygonField(
         srid=DEFAULT_SRID_RLP,
         label=_("Geometry"),
@@ -124,6 +126,38 @@ class SimpleGeomForm(BaseForm):
 
         return is_valid
 
+    def __is_vertices_num_valid(self):
+        """ Checks whether the number of vertices in the geometry is not too high
+
+        Returns:
+
+        """
+        geom = self.cleaned_data.get("geom")
+        g = gdal.OGRGeometry(geom, srs=DEFAULT_SRID_RLP)
+        num_vertices = g.num_coords
+
+        return num_vertices <= GEOM_MAX_VERTICES
+
+    def __simplify_geometry(self, geom, max_vert: int):
+        """ Simplifies a geometry
+
+        Geometry will be simplified until a threshold of max vertices has been reached.
+
+        Args:
+            geom (MultiPolygon): The geometry
+            max_vert (int): Threshold of maximum vertices in geometry
+
+        Returns:
+            geom (MultiPolygon): The simplified geometry
+        """
+        tolerance = 0.1
+        n = geom.num_coords
+        while(n > max_vert):
+            geom = geom.simplify(tolerance)
+            n = geom.num_coords
+            tolerance += 0.1
+        return geom
+
     def save(self, action: UserActionLogEntry):
         """ Saves the form's geometry
 
@@ -149,6 +183,13 @@ class SimpleGeomForm(BaseForm):
                 geom=self.cleaned_data.get("geom", MultiPolygon(srid=DEFAULT_SRID_RLP)),
                 created=action,
             )
+
+        is_vertices_num_valid = self.__is_vertices_num_valid()
+        if not is_vertices_num_valid:
+            geometry.geom = self.__simplify_geometry(geometry.geom, max_vert=GEOM_MAX_VERTICES)
+            geometry.save()
+            self.geometry_simplified = True
+
         # Start parcel update and geometry conflict checking procedure in a background process
         celery_update_parcels.delay(geometry.id)
         celery_check_for_geometry_conflicts.delay(geometry.id)