title: Django: Filtering Queryset From Two Model Fields
body: <p>My model has two fields (latitude and longitude) that I want to combine to form a point object. However, I cannot figure out how to filter based on a combination of those values:</p>
  
  <p>For example:</p>
  
  <pre><code>&gt;&gt;&gt; from django.contrib.gis.geos import Point
  &gt;&gt;&gt; lat = 5
  &gt;&gt;&gt; lon = 1
  &gt;&gt;&gt; pnt = Point(lat, lon)
  &gt;&gt;&gt; buf = pnt.buffer(0.0001)
  &gt;&gt;&gt; z = Thing.objects.filter(pnt__intersects=buf) 
  
  FieldError: Cannot resolve keyword 'pnt' into field.   ## I dont have a model field named pnt
  </code></pre>
  
  <p>I realize this is not the right approach, but I think it illustrates the problem that I am having. How can I combine two model fields — <code>lat + lon</code> — into a <code>Point</code> object then filter based on that point?</p>
  
  <hr>
  
  <p>EDIT: adding thing model</p>
  
  <pre><code>class Thing(models.Model):
      lat = models.FloatField()
      lon = models.FloatField()
  </code></pre>