Keypoints- visibility and labelling

[priyapaul]

@ZheC -could you please consider this question?
I checked the code, and I could only see that both invisible, labelled( outside segment ) and visible labelled key points((isVisible = 0,1)) are handled in the same way. Is this true? Is there any case where they are treated differently?

What about the unlabelled(isVisible = 2), key points? I see only the following code corresponding to it. Here cases isVisible = 1,2 treated in the same way, but why?

what does (isVisible = 3) stand for, is there such a case?

 if(i < 17 && meta.joint_self.isVisible[i] >= 1) {
      circle(img_vis, meta.joint_self.joints[i], 3, CV_RGB(0,0,255), -1);
    }

and also 

 if (meta.joint_self.isVisible[i] != 3){
              transformed_label[i*channelOffset + g_y*grid_x + g_x] = weight;

[tensorboy]

I also confused for that. Did you know why?