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Overview

visp_hand2eye_calibration is a ROS package that computes extrinsic camera parameters : the constant transformation from the hand to the camera coordinates.

Let's consider a camera attached to a robotic hand, as shown in the following diagram:

The interest of this package is to perform the hand to eye calibration part.

To do so, two sets of transformations are fed to the calibrator node.

• a list of camera-to-object transformations
• a list of world to hand transformations

Once the node has enough transformations, it can estimate the camera-to-hand transformation which is the goal of the calibration.

The package consists of a calibrator node and an experimental client doing a sample calibration from a few poses.

The experimental client is merely there for a quick demonstration of the package abilities.

Installation

visp_hand2eye_calibration is part of vision_visp stack.

• To install visp_hand2eye_calibration package run

  sudo apt-get install ros-$ROS_DISTRO-visp-hand2eye-calibration

• Or to install the complete stack run

  sudo apt-get install ros-$ROS_DISTRO-vision-visp

Usage

To run the calibrator node:

rosrun visp_hand2eye_calibration visp_hand2eye_calibration_calibrator

Example

An example client is shipped with this package. It feeds different transformations (camera->object and world->hand) to the calibrator which computes the relative transformation between the the camera and the hand.

To try this example, run roscore first.

roscore

Then, run the client:

rosrun visp_hand2eye_calibration visp_hand2eye_calibration_client

Finally, run the calibrator:

rosrun visp_hand2eye_calibration visp_hand2eye_calibration_calibrator

The output displayed in the terminal running your client should look like this:

[ INFO] [1329226083.184531090]: Waiting for topics...
[ INFO] [1329226084.186233704]: 1) GROUND TRUTH:
[ INFO] [1329226084.186327570]: hand to eye transformation: 
translation: 
  x: 0.1
  y: 0.2
  z: 0.3
rotation: 
  x: 0.96875
  y: 0.0863555
  z: -0.0863555
  w: 0.215889


[ INFO] [1329226085.186682976]: 2) QUICK SERVICE:
[ INFO] [1329226085.188853282]: hand_camera: 
translation: 
  x: 0.1
  y: 0.2
  z: 0.3
rotation: 
  x: 0.96875
  y: 0.0863555
  z: -0.0863555
  w: 0.215889

[ INFO] [1329226085.188915366]: 3) TOPIC STREAM:
[ INFO] [1329226085.190303537]: hand_camera: 
translation: 
  x: 0.1
  y: 0.2
  z: 0.3
rotation: 
  x: 0.96875
  y: 0.0863555
  z: -0.0863555
  w: 0.215889

Nodes

calibrator

Subscribed Topics

world_effector (visp_hand2eye_calibration/TransformArray)

• transformation between the world and the hand frame. The node expects to receive several of those transformations.

camera_object (visp_hand2eye_calibration/TransformArray)

• transformation between the camera and the object frame. The node expects to receive several of those transformations.

Services Called

compute_effector_camera (visp_hand2eye_calibration/compute_effector_camera)

• Returns the hand to camera transformation result after calibration based on the data published on the subscribed topics.

compute_effector_camera_quick (visp_hand2eye_calibration/compute_effector_camera_quick)

• Returns the hand to camera transformation result after calibration. This service is not based on the data published on the subscribed topics. Instead, the transformation are passed as service parameters.

reset (visp_hand2eye_calibration/reset)

• Reset all the data published on the subscribed topics. Only new publications (transformations) will be taken into account.