@Override
  public SensorModelResult likelihood(Context context)
      throws BadProbabilityParticleFilterException {

    final VehicleState state = context.getState();
    final VehicleState parentState = context.getParentState();
    final Observation obs = context.getObservation();
    final EVehiclePhase phase = state.getJourneyState().getPhase();
    final BlockStateObservation blockStateObs = state.getBlockStateObservation();

    //    /*-
    //     * TODO clean up this hack
    //     * We are really in-progress, but because of the
    //     * out-of-service headsign, we can't report it as in-progress
    //     */
    //    if (obs.hasOutOfServiceDsc() && EVehiclePhase.DEADHEAD_DURING == phase
    //        && (blockStateObs != null && blockStateObs.isOnTrip()))
    //      phase = EVehiclePhase.IN_PROGRESS;

    final SensorModelResult result = new SensorModelResult("pEdge", 1d);

    if (obs.getPreviousObservation() == null || parentState == null) {
      if (EVehiclePhase.isActiveDuringBlock(phase)) {
        result.addResultAsAnd("no prev. obs./vehicle-state(in-progress)", 1d);
      } else {
        result.addResultAsAnd("no prev. obs./vehicle-state", 1d);
      }
      return result;
    }

    if (obs.isAtBase()) {
      result.addResultAsAnd("pNotInProgress(base)", 1d);
      return result;
    }

    if (blockStateObs == null) {

      result.addResultAsAnd(computeNoEdgeMovementLogProb(state, obs));
      return result;
    }

    /*
     * Edge Movement
     */
    final boolean previouslyInactive = parentState.getBlockState() == null;
    final boolean newRun =
        MotionModelImpl.hasRunChanged(
            parentState.getBlockStateObservation(), state.getBlockStateObservation());

    final boolean hasMoved = !state.getMotionState().hasVehicleNotMoved();
    if (!previouslyInactive && !newRun) {

      /*
       * This could be a transition from being on a trip geom to off, and vice
       * versa.
       */
      if (EVehiclePhase.IN_PROGRESS != phase) {
        /*
         * We're currently not in-progress
         */
        if (EVehiclePhase.isActiveDuringBlock(phase)) {
          if (state
              .getBlockState()
              .getBlockInstance()
              .equals(parentState.getBlockState().getBlockInstance())) {
            result.addResultAsAnd(
                computeEdgeMovementLogProb(obs, state, parentState, hasMoved, true));
          } else {
            result.addResultAsAnd(computeNoEdgeMovementLogProb(state, parentState, obs));
          }
        } else {
          result.addResultAsAnd(computeNoEdgeMovementLogProb(state, obs));
        }
      } else if (EVehiclePhase.IN_PROGRESS != parentState.getJourneyState().getPhase()) {
        /*
         * We were previously not in-progress, and now we are.
         */
        if (EVehiclePhase.isActiveDuringBlock(parentState.getJourneyState().getPhase())) {
          result.addResultAsAnd(
              computeEdgeMovementLogProb(obs, state, parentState, hasMoved, true));
        } else {
          result.addResultAsAnd(computeNoEdgeMovementLogProb(state, parentState, obs));
        }
      } else {
        /*
         * We're in-progress and were before.
         */
        result.addResultAsAnd(computeEdgeMovementLogProb(obs, state, parentState, hasMoved, false));
      }

    } else {
      /*
       * We have a new run, or just got one after having nothing.
       */

      if (EVehiclePhase.IN_PROGRESS == phase) {
        if (EVehiclePhase.isActiveDuringBlock(parentState.getJourneyState().getPhase())) {
          result.addResultAsAnd(
              computeEdgeMovementLogProb(obs, state, parentState, hasMoved, false));
        } else {
          result.addResultAsAnd(computeNoEdgeMovementLogProb(state, parentState, obs));
        }

      } else {
        result.addResultAsAnd(computeNoEdgeMovementLogProb(state, obs));
      }
    }

    return result;
  }
  private static final SensorModelResult computeNoEdgeMovementLogProb(
      VehicleState state, VehicleState prevState, Observation obs)
      throws BadProbabilityParticleFilterException {

    final SensorModelResult result = new SensorModelResult("no-edge");
    final Observation prevObs = obs.getPreviousObservation();
    final double obsDistDelta = obs.getDistanceMoved();

    if (ParticleFilter.getDebugEnabled()) result.addResult("dist: " + obsDistDelta, 0d);

    final double expAvgDist;
    final double logpDistAlong;
    if (prevObs != null) {

      /*
       * Trying to get away with not using a real tracking filter.
       * FIXME really lame. use a Kalman filter.
       */
      final double obsTimeDelta = obs.getTimeDelta();
      if (prevObs.getTimeDelta() != null) {
        final double prevObsDistDelta = prevObs.getDistanceMoved();
        final double prevObsTimeDelta = prevObs.getTimeDelta();
        final double velocityEstimate = prevObsDistDelta / prevObsTimeDelta;
        expAvgDist =
            state.getMotionState().hasVehicleNotMoved() ? 0d : velocityEstimate * obsTimeDelta;
      } else {
        expAvgDist = state.getMotionState().hasVehicleNotMoved() ? 0d : _avgVelocity * obsTimeDelta;
      }

      if (ParticleFilter.getDebugEnabled()) result.addResult("expAvgDist: " + expAvgDist, 0d);

      /*
       * TODO: Is this needed?
       */
      final boolean prevInProgress;
      double prevOrientation;
      if (prevState != null
          && prevState.getBlockState() != null
          && prevState.getJourneyState().getPhase() == EVehiclePhase.IN_PROGRESS) {
        prevOrientation = prevState.getBlockState().getBlockLocation().getOrientation();
        prevInProgress = true;
        if (ParticleFilter.getDebugEnabled())
          result.addResult("prevOrient (state): " + prevOrientation, 0d);
      } else {
        prevOrientation = prevObs.getOrientation();
        prevInProgress = false;
        if (ParticleFilter.getDebugEnabled())
          result.addResult("prevOrient: " + prevOrientation, 0d);
      }

      final boolean isOff;
      final double currentOrientation;
      if (state.getBlockState() != null
          && state.getJourneyState().getPhase() == EVehiclePhase.IN_PROGRESS) {
        /*
         * We're entering an edge in progress, so we want to compare the
         * entrance orientation to the direction of the edge
         */
        isOff = false;
        currentOrientation = state.getBlockState().getBlockLocation().getOrientation();
        /*
         * We don't want to use the obs orientation when we're considered stopped
         * since gps error can reverse the orientation, making reverse
         * trip transitions look reasonable.
         * Similarly, if we were on a trip, use that orientation.
         * TODO FIXME: we should have the orientation in the motion state, then
         * we wouldn't need to evaluate this logic here.
         */
        if (!state.getMotionState().hasVehicleNotMoved()) {
          if (!prevInProgress) {
            prevOrientation = obs.getOrientation();
          }

          if (ParticleFilter.getDebugEnabled())
            result.addResult("new prevOrient (state): " + prevOrientation, 0d);
        }
      } else {
        isOff = true;
        currentOrientation = obs.getOrientation();
      }

      if (ParticleFilter.getDebugEnabled())
        result.addResult("curOrient: " + currentOrientation, 0d);

      final double orientDiff;
      if (Double.isNaN(prevOrientation) || Double.isNaN(currentOrientation)) {
        orientDiff = 0d;
      } else {
        orientDiff =
            Angle.diff(Math.toRadians(prevOrientation), Math.toRadians(currentOrientation));
      }

      logpDistAlong =
          UnivariateGaussian.PDF.logEvaluate(
                  obsDistDelta, expAvgDist, Math.pow(obsTimeDelta, 4) / 4d)
              + (isOff
                  ? _deadheadOffProb * logVonMisesPdf(orientDiff, _deadheadConcParam)
                  : _inProgressProb * logVonMisesPdf(orientDiff, _deadheadEntranceConcParam));

    } else {
      /*
       * No movement
       */
      logpDistAlong = 1d;
    }

    result.addLogResultAsAnd("lik", logpDistAlong);

    return result;
  }