Is there a bug in show function of Robotics System Toolbox of 2021a version?

It seems there is a bug in `show` function.

This is a simple robot model built using DH parameters.

dhparams = [0   	pi/2	0   	0;
    0.4318	0       0       0
    0.0203	-pi/2	0.15005	0;
    0   	pi/2	0.4318	0;
    0       -pi/2	0   	0;
    0       0       0       0];
robot = rigidBodyTree;
body1 = rigidBody('body1');
jnt1 = rigidBodyJoint('jnt1','revolute');

setFixedTransform(jnt1,dhparams(1,:),'dh');
body1.Joint = jnt1;

addBody(robot,body1,'base')
body2 = rigidBody('body2');
jnt2 = rigidBodyJoint('jnt2','revolute');
body3 = rigidBody('body3');
jnt3 = rigidBodyJoint('jnt3','revolute');
body4 = rigidBody('body4');
jnt4 = rigidBodyJoint('jnt4','revolute');
body5 = rigidBody('body5');
jnt5 = rigidBodyJoint('jnt5','revolute');
body6 = rigidBody('body6');
jnt6 = rigidBodyJoint('jnt6','revolute');

setFixedTransform(jnt2,dhparams(2,:),'dh');
setFixedTransform(jnt3,dhparams(3,:),'dh');
setFixedTransform(jnt4,dhparams(4,:),'dh');
setFixedTransform(jnt5,dhparams(5,:),'dh');
setFixedTransform(jnt6,dhparams(6,:),'dh');

body2.Joint = jnt2;
body3.Joint = jnt3;
body4.Joint = jnt4;
body5.Joint = jnt5;
body6.Joint = jnt6;

addBody(robot,body2,'body1')
addBody(robot,body3,'body2')
addBody(robot,body4,'body3')
addBody(robot,body5,'body4')
addBody(robot,body6,'body5')
showdetails(robot)

show(robot);
axis([-0.5,0.5,-0.5,0.5,-0.5,0.5])
axis off

But there are something wrong with the figure ploted by show funciton: when I click the axis of some body, the arrow that shows the revolute direction is not coinside with the axis, just like this

When I click the body 3, is shows the z axis of body 2, and when I click the body2, it shows the z axis of body1.

So, is there a bug of show function? Because the show funciton in MATLAB 2020a is normal.

Answer 1

[Yiping Liu]

So the plot from 20a (LEFT) is incorrect, and this bug has been fixed in 21a (the plot on the RIGHT shows the correct joint axis).

For a robot specified using DH parameters, when you click on body3, its rotation axis happens to be aligned with the z axis of body2's body frame.