Walker Bone Control

In this tutorial we describe how to manually control and animate the skeletons of walkers from the CARLA Python API. The reference of all classes and methods available can be found at Python API reference.

Note

This document assumes the user is familiar with the Python API.
The user should read the Python API tutorial before reading this document. Python API tutorial.

Walker skeleton structure

All walkers have the same skeleton hierarchy and bone names. Below is an image of the skeleton hierarchy.

crl_root
└── crl_hips__C
    ├── crl_spine__C
    │   └── crl_spine01__C
    │       ├── ctrl_shoulder__L
    │       │   └── crl_arm__L
    │       │       └── crl_foreArm__L
    │       │           └── crl_hand__L
    │       │               ├── crl_handThumb__L
    │       │               │   └── crl_handThumb01__L
    │       │               │       └── crl_handThumb02__L
    │       │               │           └── crl_handThumbEnd__L
    │       │               ├── crl_handIndex__L
    │       │               │   └── crl_handIndex01__L
    │       │               │       └── crl_handIndex02__L
    │       │               │           └── crl_handIndexEnd__L
    │       │               ├── crl_handMiddle_L
    │       │               │   └── crl_handMiddle01__L
    │       │               │       └── crl_handMiddle02__L
    │       │               │           └── crl_handMiddleEnd__L
    │       │               ├── crl_handRing_L
    │       │               │   └── crl_handRing01__L
    │       │               │       └── crl_handRing02__L
    │       │               │           └── crl_handRingEnd__L
    │       │               └── crl_handPinky_L
    │       │                   └── crl_handPinky01__L
    │       │                       └── crl_handPinky02__L
    │       │                           └── crl_handPinkyEnd__L
    │       ├── crl_neck__C
    │       │   └── crl_Head__C
    │       │       ├── crl_eye__L
    │       │       └── crl_eye__R
    │       └── crl_shoulder__R
    │           └── crl_arm__R
    │               └── crl_foreArm__R
    │                   └── crl_hand__R
    │                       ├── crl_handThumb__R
    │                       │   └── crl_handThumb01__R
    │                       │       └── crl_handThumb02__R
    │                       │           └── crl_handThumbEnd__R
    │                       ├── crl_handIndex__R
    │                       │   └── crl_handIndex01__R
    │                       │       └── crl_handIndex02__R
    │                       │           └── crl_handIndexEnd__R
    │                       ├── crl_handMiddle_R
    │                       │   └── crl_handMiddle01__R
    │                       │       └── crl_handMiddle02__R
    │                       │           └── crl_handMiddleEnd__R
    │                       ├── crl_handRing_R
    │                       │   └── crl_handRing01__R
    │                       │       └── crl_handRing02__R
    │                       │           └── crl_handRingEnd__R
    │                       └── crl_handPinky_R
    │                           └── crl_handPinky01__R
    │                               └── crl_handPinky02__R
    │                                   └── crl_handPinkyEnd__R
    ├── crl_thigh__L
    │   └── crl_leg__L
    │       └── crl_foot__L
    │           └── crl_toe__L
    │               └── crl_toeEnd__L
    └── crl_thigh__R
        └── crl_leg__R
            └── crl_foot__R
                └── crl_toe__R
                    └── crl_toeEnd__R

How to manually control a walker's bones

Following is a detailed step-by-step example of how to change the bone transforms of a walker from the CARLA Python API

Connecting to the simulator

Import neccessary libraries used in this example

import carla
import random

Initialize the carla client

client = carla.Client('127.0.0.1', 2000)
client.set_timeout(2.0)

Spawning a walker

Spawn a random walker at one of the map's spawn points

world = client.get_world()
blueprint = random.choice(self.world.get_blueprint_library().filter('walker.*'))
spawn_points = world.get_map().get_spawn_points()
spawn_point = random.choice(spawn_points) if spawn_points else carla.Transform()
world.try_spawn_actor(blueprint, spawn_point)

Controlling a walker's skeleton

A walker's skeleton can be modified by passing an instance of the WalkerBoneControl class to the walker's apply_control function. The WalkerBoneControl class contains the transforms of the bones to be modified. Its bone_transforms member is a list of tuples of value pairs where the first value is the bone name and the second value is the bone transform. The apply_control function can be called on every tick to animate a walker's skeleton. The location and rotation of each transform is relative to its parent. Therefore when a parent bone's transform is modified, the transforms of the child bones in model space will also be changed relatively.

In the example below, the rotations of the walker's hands are set to be 90 degrees around the forward axis and the locations are set to the origin.

control = carla.WalkerBoneControl()
first_tuple = ('crl_hand__R', carla.Transform(rotation=carla.Rotation(roll=90)))
second_tuple = ('crl_hand__L', carla.Transform(rotation=carla.Rotation(roll=90)))
control.bone_transforms = [first_tuple, second_tuple]
world.player.apply_control(control)