# Revision history [back]

### AMCL Covariance : define a "good" covariance

Hello,

hello,I am using AMCL to localize my robot. When i suscribe to /amcl_pose, I get some geometry_msgs::StampedPoseWithCovariance.

I read a lot about AMCL and covariance and I understood what lines of the matrix represent (Position X,Y,Z and Rotation X,Y,Z) => Only position(X,Y) and Rotation(Z) are non null/usefull as my robot is not flying. This thread which contain usefull informations.

I now hace 2 questions and found only partial informations: 1) Are the covariance sent by amcl_pose relative to the last update (eg. at T1 covariance is relative to T0) 2) What define a "good covariance"? A threshold on values? How to determine it?

### AMCL Covariance : define a "good" covariance

Hello,

hello,I am using AMCL to localize my robot. When i suscribe to /amcl_pose, I get some geometry_msgs::StampedPoseWithCovariance.

I read a lot about AMCL and covariance and I understood what lines of the matrix represent (Position X,Y,Z and Rotation X,Y,Z) => Only position(X,Y) and Rotation(Z) are non null/usefull as my robot is not flying. This thread which contain usefull informations.

I now hace 2 questions and found only partial informations:
1) Are the covariance sent by amcl_pose relative to the last update (eg. at T1 covariance is relative to T0) T0)
2) What define a "good covariance"? A threshold on values? How to determine it?it?