How confidence is calculated in pose estimation without a reference (truth) keypoint

Hello,

we would like to ask what the confidence index means and how it is calculated without knowing any reference (truth) keypoint.

We applied the following pose estimation model:

https://cv.gluon.ai/build/examples_pose/demo_simple_pose.html

In this model we predicted the pose of a new picture. The model predicted the keypoints and provided a confidence. Unfortunately we dont know how the model calculates the confidence.

Thank you for the help!