base frame for URDF, SRDF, Gazebo

[jacknlliu]

Gazebo needs world frame and MoveIt need a virtual fixed joint with a link.

The urdf of an industrial robot needs a base frame.

base_link of ROS-I: The base_link shall be positioned in the logical base position (oriented by convention, z-axis up, x-axis forward). This frame name is by ROS convention. Typically this frame is the first frame of the robot tied to the first link.

Reference

• Rename 'world' frame to 'robot_base' in URDF
• Skipping virtual joint 'fixed_base' because its child frame 'base_link' does not match the URDF frame 'world'
• Create a URDF for an Industrial Robot