Gazebo Ignition: Unable to create message of type[gz.msgs.Twist] with data

Question

I am following the tutorial : https://gazebosim.org/docs/all/moving_robot/ on the official website of gazebo.

However when I try to run the command ign topic -t /cmd_vel -m gz.msgs.Twist -p "linear {x: 0.5, y: 0.0, z: 0.0}, angular {x: 0.0, y: 0.0, z: 0.05}" or gz topic -t /cmd_vel -m gz.msgs.Twist -p "linear {x: 0.5, y: 0.0, z: 0.0}, angular {x: 0.0, y: 0.0, z: 0.05}" I get an error stating :

ign topic -t /cmd_vel -m ign.msgs.Twist -p "linear {x: 0.5, y: 0.0, z: 0.0}, angular {x: 0.0, y: 0.0, z: 0.05}"

I tried many times following the tutorial again to see if I missed anything but it looks like all the steps are right

If I try to use the command gz topic -t "/cmd_vel" -m gz.msgs.Twist -p "linear: {x: 0.5}, angular: {z: 0.05}" I get "Invalid Arguments"

Has anyone faced this issue?

Answer 1

There's "Gazebo Classic", i.e. 'Old Gazebo', and "Gazebo Sim", i.e. 'new Gazebo'.

Gazebo Sim was initially called Ignition, up until version 6 (Fortress). From version 7 (Humble) on, Ignition had to be renamed due to a trademark issue. It was renamed to Gazebo Sim.

Ignition came with bash command ign and ignition.msgs.Twist types. In Gazebo Sim, these were renamed to gz and gz.msgs.Twist.

You seem to be intermingling these, as well as using ign.msgs.Twist instead of ignition.msgs.Twist.

I checked the tutorial you link to, but if you select Fortress as the version (selection box top right), it correctly shows following syntax:

ign topic -t "/cmd_vel" -m ignition.msgs.Twist -p "linear: {x: 0.5}, angular: {z: 0.05}"

See also the example worlds, more specifically here.