lost-detector.md

layout	title	category	tags
reference	lost_detector	node	lost detector amcl localization

Description

The lost_detector node looks at the spread of particles from amcl and tries to decide whether the robot might be confused or lost.

The lost detector creates two features based on the amcl particle filter spread. The first is the standard deviation of the longest dimension of the x-y covariance ellipse (where the longest dimension corresponds to the largest eigenvector of the covariance matrix), and the second is the standard deviation of the particles' theta values.

Those two features are used each time amcl broadcasts its particle covariance, to evaluate whether the robot currently looks "lost" or "normal" using a Gaussian Naive Bayes (GNB) classifier. If enough time steps recently have looked "lost," then the lost_detector will declare the robot confused or lost.

In particular, /lost_detector/status outputs one of the following:
"confused" (tier 1): we've seen at least lost_detector/queue_min detections and this reading was labeled lost by the GNB classifier

"lost" (tier 2): the ratio of lost to normal readings in the last lost_detector/window_meta_tier2_lost readings is higher than lost_detector/ratio_thresh_detections_tier2_lost

"normal" (tier 0): neither confused nor lost

Seeing lost_detector/window_meta_tier0_normal "normal" readings will reset the lost detector entirely.

Dependencies

• amcl
• lots of other things brought in by gizmo

Subscribed Topics

/lost_detector/reset

std_msgs::Empty
Used to reset the lost detector (empty queue, set status to normal)

/laser_amcl_pose
geometry_msgs::PoseWithCovarianceStamped
Used to get the covariance matrix from amcl

Published Topics

/lost_detector/status

std_msgs/String
Outputs "lost," "confused," or "normal" depending on the state of the lost_detector

Parameters

Parameters can be found in gizmo/app/configs/lost_detector.yaml.
In namespace modified_prob_classifier (params for the GNB classifier):

modified_prob_classifier/tier0_normal_prior

double
The prior on whether we are lost

modified_prob_classifier/prob_thresh

double
Classify this single set of features as "lost" if the prob is > prob_thresh that it belongs to the lost-gaussian

modified_prob_classifier/slice_mu

4-vector of doubles
mu (mean) vector is: [xy-not-lost, theta-not-lost, xy-lost, theta-lost]
units are meters, radians

modified_prob_classifier/slice_sigma

4-vector of doubles
sigma vector is: [xy-std-not-lost, theta-std-not-lost, xy-std-lost, theta-std-lost]
units are meters, radians

In namespace lost_detector:

lost_detector/window_meta_tier2_lost

int
how many lost detections to track when deciding whether we're tier2 "lost"

lost_detector/window_meta_tier0_normal

int
if we haven't looked lost this many times in a row, declare that we're no longer lost (reset queue and set to detector to normal)

lost_detector/queue_min

int
min length of detection queue before we will declare even tier1 "confused"

lost_detector/ratio_thresh_detections_tier2_lost

double
if the ratio of lost detections in the queue is this high, we are tier2 "lost"

Launch File

lost_detector pylaunch