modify modelconverter to support GeoPtProperty of appengine

flask_admin/contrib/appengine/fields.py

+from wtforms.fields import TextField
+from google.appengine.ext import ndb
+
+import decimal
+
+class GeoPtPropertyField(TextField):
+    def process_formdata(self, valuelist):
+        if valuelist:
+            try:
+                lat, lon = valuelist[0].split(',')
+                self.data = ndb.GeoPt(
+                    decimal.Decimal(lat.strip()),
+                    decimal.Decimal(lon.strip())
+                )
+
+            except (decimal.InvalidOperation, ValueError):
+                raise ValueError('Not a valid coordinate location')

flask_admin/contrib/appengine/form.py

+from wtforms_appengine.ndb import ModelConverter
+from .fields import GeoPtPropertyField
+from flask_admin.model.form import converts
+
+class AdminModelConverter(ModelConverter):
+    @converts('GeoPt')
+    def convert_GeoPtProperty(self, model, prop, kwargs):
+        """Returns a form field for a ``ndb.GeoPtProperty``."""
+        return GeoPtPropertyField(**kwargs)