Extrinsic calibration

This a short tutorial for extrinsic calibration of Pepper's Depth and RGB cameras.

Setup

First of all, print a calibration pattern (a chessboard) if you do not have any. We would recommend A3 size. Once you have it, count the number of rows and columns and measure a size of a square. Adjust these parameters in launch/calibration_cameras_pepper.launch:

define the numbers of columns -1
define the numbers of rows -1
define the size of one square in m

Data recording

turn on your robot, wake up, and move the head to the "zero" pose, for example

ssh nao@<PEPPER_IP>
qicli call ALMotion.wakeUp
qicli call ALMotion.setAngles "HeadPitch" 0.0 0.3

take two post-it (one on the top of enougher) and fix it on the right eye of Pepper (to cover this eye with the camera inside)
start Naoqi Driver, ensuring that color and IR images are enabled in share/boot_config.json

roslaunch naoqi_driver naoqi_driver.launch nao_ip:=<PEPPER_IP>

create an empty folder for data recording and provide its name in launch/extrinsic_calibration_pepper.launch
update ROS topics for color and IR images in launch/extrinsic_calibration_pepper.launch
launch the code:

roslaunch extrinsic_calibration extrinsic_calibration_pepper.launch

if the software can subscribe to ROS topics, then you should see an image from a color camera
place the calibration pattern in front of the robot
once the pattern is detected (you can see all detected crossings), press "s" on your keyboard to save images from both cameras
repeat 2 previous steps each time changing a distance and/or an angle to cover different views (at 60cm-80m distance) until you reach a sufficient number of image pairs (for example, 30 times or more)

Calibration based on recorded data

launch the code to compute extrinsic parameters based on recorded images:

roslaunch extrinsic_calibration extrinsic_calibration_pepper.launch

press "c" on your keyboard to compute calibration values
check if the resulted XYZ and RPY for last processed image pair correspond to the reality

The extrinsic parameters obtained for our Pepper are:

XYZ: 0.0708098 0.02 0.118115
RPY: -1.5936 -0.0161345 -1.57777

How to update the extrinsic parameters in URDF of your robot

There are two possible ways to applying the extrinsic parameters:

using ROS static_transform_publisher
updating the position of the camera in the URDF

Using static_transform_publisher

An example of using static_transform_publisher is shown in register_depth.launch of Naoqi Driver. You can update the values in register_depth.launch in your workspace. The order of the values is: x y z yaw pitch roll. Once updted, launch this file in addition to naoqi_driver:

roslaunch naoqi_driver naoqi_driver.launch nao_ip:=<PEPPER_IP>
roslaunch naoqi_driver register_depth.launch

Using URDF

Alternatively, you can update the parameters directly in the URDF file:

update RPY values in https://github.com/nlyubova/pepper_robot/blob/master/pepper_description/urdf/pepper1.0_generated_urdf/pepper_sensors.xacro#L23
update XYZ values in https://github.com/nlyubova/pepper_robot/blob/master/pepper_description/urdf/pepper1.0_generated_urdf/pepper_sensors.xacro#L120
generate a new pepper.URDF file, for example

roscd pepper_description
cd urdf/pepper1.0_generated_urdf/
rosrun xacro xacro.py -o pepper.urdf pepper_robot.xacro

start Naoqi Driver as usual