Prevent track from birth component w/o detection

docs/tutorials/11_GMPHDTutorial.py

@@ -332,7 +332,7 @@
             state_vector=truth.state_vector,
             covar=covar**2,
             weight=0.25,
-            tag='birth',
+            tag=TaggedWeightedGaussianState.BIRTH,
             timestamp=start_time)
     tracks.add(Track(new_track))
 

stonesoup/hypothesiser/gaussianmixture.py

@@ -5,6 +5,7 @@
 from ..types.prediction import (TaggedWeightedGaussianStatePrediction,
                                 WeightedGaussianStatePrediction)
 from ..types.state import TaggedWeightedGaussianState
+from ..types.detection import MissedDetection
 
 
 class GaussianMixtureHypothesiser(Hypothesiser):
@@ -59,10 +60,18 @@ def hypothesise(self, components, detections, timestamp, **kwargs):
                                                                  **kwargs)
             for hypothesis in component_hypotheses:
                 if isinstance(component, TaggedWeightedGaussianState):
+                    # Ensure that a birth component without a measurement retains
+                    # the birth tag. This will prevent a track from being made
+                    if component.tag == component.BIRTH and \
+                            isinstance(hypothesis.measurement, MissedDetection):
+                        tag = component.BIRTH
+                    elif component.tag == component.BIRTH:
+                        tag = None  # a new tag will be made
+                    else:
+                        tag = component.tag
                     hypothesis.prediction = \
                         TaggedWeightedGaussianStatePrediction(
-                            tag=component.tag if component.tag != "birth"
-                            else None,
+                            tag=tag,
                             weight=component.weight,
                             state_vector=hypothesis.prediction.state_vector,
                             covar=hypothesis.prediction.covar,

stonesoup/tracker/pointprocess.py

@@ -31,7 +31,9 @@ class PointProcessMultiTargetTracker(Tracker):
         default=None,
         doc="The birth component. The weight should be "
             "equal to the mean of the expected number of "
-            "births per timestep (Poission distributed)")
+            "births per timestep (Poission distributed). "
+            "The tag should be "
+            ":attr:`TaggedWeightedGaussianState.BIRTH`")
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
@@ -64,8 +66,7 @@ def update_tracks(self):
         """
         for component in self.gaussian_mixture:
             tag = component.tag
-            if tag != 0:
-                # Sanity check for birth component
+            if tag != component.BIRTH:  # Sanity check for birth component
                 if tag in self.target_tracks:
                     # Track found, so update it
                     track = self.target_tracks[tag]

stonesoup/tracker/tests/test_pointprocess.py

@@ -23,7 +23,7 @@ def test_point_process_multi_target_tracker_cycle(detector, predictor):
         birth_mean,
         birth_covar,
         weight=0.3,
-        tag="birth",
+        tag=TaggedWeightedGaussianState.BIRTH,
         timestamp=timestamp)
 
     # Initialise a Kalman Updater

stonesoup/types/state.py

@@ -420,6 +420,9 @@ class TaggedWeightedGaussianState(WeightedGaussianState):
     """
     tag: str = Property(default=None, doc="Unique tag of the Gaussian State.")
 
+    BIRTH = 'birth'
+    '''Tag value used to signify birth component'''
+
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         if self.tag is None: