How to change the color of a rigidbody visual.

Hello,

I am creating a rigid body (robot link) and would like to change the color of the visual. For example:

body1 = rigidBody('body1');
jnt1 = rigidBodyJoint('jnt1','revolute');
tform = trvec2tform([0 1 0]); 
setFixedTransform(jnt1,tform);
body1.Joint = jnt1;
robot = rigidBodyTree('DataFormat', 'column');
addVisual(body1, "sphere", 1.2)
addBody(robot,body1,'base')  
show(robot,"Visuals", "on", 'Frames', 'off')

It always generates the figure in gray scale. I would like to assign a different color to different bodies. How can I do that? I know that I can also add collision boxes or spheres, but they are similarly of the same color by default (green).

Answer 1

[Chunru]

body1 = rigidBody('body1');
jnt1 = rigidBodyJoint('jnt1','revolute');
tform = trvec2tform([0 1 0]); 
setFixedTransform(jnt1,tform);
body1.Joint = jnt1;
robot = rigidBodyTree('DataFormat', 'column');
addVisual(body1, "sphere", 1.2)
addBody(robot,body1,'base')  
g = show(robot,"Visuals", "on", 'Frames', 'off');
% You can change color of individual object
g.Children(1).FaceColor = 'r';

[Control Systems Guy]

This is great! Thank you very much! I still have 2 questions/problems I would like an answer.

1) Is there a way to change the color of all bodies at once? Something like: g.Children(1:end).FaceColor

For example, if I have a robot (rigidbody) with two links:

body1 = rigidBody('body1');
jnt1 = rigidBodyJoint('jnt1','revolute');
tform = trvec2tform([0 1 0]); 
setFixedTransform(jnt1,tform);
body1.Joint = jnt1;
robot = rigidBodyTree('DataFormat', 'column');
addVisual(body1, "sphere", 1.2)
addBody(robot,body1,'base')  

body2 = rigidBody('body2');
jnt2 = rigidBodyJoint('jnt2','revolute');
tform2 = trvec2tform([1, 0, 0]); 
setFixedTransform(jnt2,tform2);
body2.Joint = jnt2;
addVisual(body2, "capsule", [.5, 3],[0 0 1 0; 0 1 0 0; -1 0 0 0; 0 0 0 1])
addBody(robot,body2,'body1'); % Add body2 to body1

figure(1)
g = show(robot,"Visuals", "on", 'Frames', 'off');
g.Children(1).FaceColor = 'r';

2) Can I make the color change permanent? I am working with a robot of multiple links that will rotate and move, and I would like to avoid having to change the color at each step of the animation.

Once again, thank you!

Answer 2

[Chunru]

See below for the question (1). I am not sure the part (2) and you may want to show your current code.

body1 = rigidBody('body1');
jnt1 = rigidBodyJoint('jnt1','revolute');
tform = trvec2tform([0 1 0]); 
setFixedTransform(jnt1,tform);
body1.Joint = jnt1;
robot = rigidBodyTree('DataFormat', 'column');
addVisual(body1, "sphere", 1.2)
addBody(robot,body1,'base')  
body2 = rigidBody('body2');
jnt2 = rigidBodyJoint('jnt2','revolute');
tform2 = trvec2tform([1, 0, 0]); 
setFixedTransform(jnt2,tform2);
body2.Joint = jnt2;
addVisual(body2, "capsule", [.5, 3],[0 0 1 0; 0 1 0 0; -1 0 0 0; 0 0 0 1])
addBody(robot,body2,'body1'); % Add body2 to body1
figure(1)
g = show(robot,"Visuals", "on", 'Frames', 'off');

% Change color for all applicable children
for i=1:length(g.Children)
    try
        g.Children(i).FaceColor = 'r';
    end
end

[Control Systems Guy]

Chunru, thanks again for helping me out. What I meant by the 2nd question is that I would like to avoid having to specificy the FaceColor every single time I call the robot again. For example:

body1 = rigidBody('body1');
jnt1 = rigidBodyJoint('jnt1','revolute');
tform = trvec2tform([0 1 0]); 
setFixedTransform(jnt1,tform);
body1.Joint = jnt1;
robot = rigidBodyTree('DataFormat', 'column');
addVisual(body1, "sphere", 1.2)
addBody(robot,body1,'base')  
body2 = rigidBody('body2');
jnt2 = rigidBodyJoint('jnt2','revolute');
tform2 = trvec2tform([1, 0, 0]); 
setFixedTransform(jnt2,tform2);
body2.Joint = jnt2;
addVisual(body2, "capsule", [.5, 3],[0 0 1 0; 0 1 0 0; -1 0 0 0; 0 0 0 1])
addBody(robot,body2,'body1'); % Add body2 to body1
figure(1)
g = show(robot,"Visuals", "on", 'Frames', 'off');
% Change color for all applicable children
for i=1:length(g.Children)
    try
        g.Children(i).FaceColor = 'r';
    end
end

for k = 1:5
    q = [k/5; 0];
    g = show(robot,q,"Visuals", "on", 'Frames', 'off');
    drawnow
end

If I used one of the predefined robot models, I see that some models have a different color (other than gray) specified by default. In the following example, one doesnt need to speficy the color every single time I want to update the robot configuration. Maybe rather than using "show" I can use "set(robot,...)?

figure(2)
robot2 = importrobot('iiwa14.urdf');
robot2.DataFormat = "column";
for k = 1:5
    q = [0 0 0 k*pi/10 0 0 pi/2]';
    g = show(robot2,q,"Visuals", "on", "Frames","off");
    drawnow
end