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An incomprehension about geometry_msgs/PoseWithCovariance Message

asked 2020-02-26 06:59:49 -0500

YancenBOB
9 ●9 ●12 ●15

Hi, I have a question about pose covariance.

In the doc website (link text), I see the covariance is shown as a matrix with 6*6 size and the parameters are x, y, z, rotation about X axis, rotation about Y axis, rotation about Z axis in order.

I am confused about the size and the parameters. The x,y,z are the coordinate of a 3D point and they are 3 parameters? And then, three rotations are shown in 33 matrix respectively? If it is, the all parameters are 3 + 39 = 30. Why 6*6 here?

Thank you!

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answered 2020-02-26 10:34:16 -0500

bob-ROS

525 ●3 ●49 ●12

updated 2020-02-26 10:44:12 -0500

It is 6x6 because it is a covariance matrix with the 6 different states ( x, y, z, roll, pitch, yaw). The diagonal of this matrix is the variance ( the "spread" of a specific state, e.g. a high x position variance means it has a very large spread of values), the other values will be the "covariance" with respect to the other 5 states. If it is a pure diagonal matrix it means there is no covariance between the states.

https://datascienceplus.com/understan...