code: private void removeMarkedObservations() {
  		Point2D_F64 observation = new Point2D_F64();
  
  		for (int viewIndex = 0; viewIndex < observations.views.length; viewIndex++) {
  //			System.out.println("ViewIndex="+viewIndex);
  			SceneObservations.View v = observations.views[viewIndex];
  			for(int indexInView = v.point.size-1; indexInView >= 0; indexInView-- ) {
  				int pointID = v.getPointId(indexInView);
  				SceneStructureProjective.Point f = structure.points[pointID];
  //				System.out.println("   pointIndex="+pointIndex+" pointID="+pointID+" hash="+f.hashCode());
  				v.get(indexInView, observation);
  
  				if( !Double.isNaN(v.observations.get(indexInView*2)))
  					continue;
  
  				// Tell the feature it is no longer visible in this view
  				f.removeView(viewIndex);
  				// Remove the observation of this feature from the view
  				v.remove(indexInView);
  			}
  		}
  	}
docs: Removes observations which have been marked with NaN