Main methods¶
Main methods to use the tracker are startTracker() / stopTracker().
NAOqi Trackers¶
Overview | ALRedBallTracker API | ALFaceTracker API | Trackers Sample
What it does¶
The Tracker modules allow you to make NAO track targets (a red ball or a face).
The main goal of these modules is to establish a bridge between target detection and motion in order to make NAO keep in view the target in the middle of the camera.
How it works¶
Step by step¶
A - Starts the tracker by Subscribing to Event TargetDetected from ALTargetDetection module (ALRedBallTrackerProxy::startTracker or ALFaceTrackerProxy::startTracker).
B - Waits Event TargetDetected from ALTargetDetection module.
C - When target is detected, sends information to motion of the position of the new target (ALMotionProxy::updateTrackerTarget).
D - Stops the tracker by Unsubscribing to Event TargetDetected from ALTargetDetection module (ALRedBallTrackerProxy::stopTracker, ALFaceTrackerProxy::stopTracker).
Position identification¶
- The Tracker modules (ALRedBallTracker, ALFaceTracker) identify the position of target (“Red ball” or “Face”) seen by NAO.
- It can give the position of the target in SPACE_TORSO (see Spaces about the different spaces).
- Function getPosition returns the [x, y, z] position of the target (ALRedBallTracker::ALRedBallTrackerProxy::getPosition or ALFaceTracker::ALFaceTrackerProxy::getPosition).
Performance and Limitations¶
Limitations
You can use only top camera.
This is done assuming an average target size, so it might not be very accurate.
Getting started¶
Prerequisite¶
- These modules need respectively ALRedBallDetection and ALFaceDetection module to run. So be sure it is loaded on your robot.
- Stiffness of Head must be set to 1.0 to move. Use motion api ALMotionProxy::stiffnessInterpolation.
Settings¶
Choose the kind of motion tracking using the following api: (ALRedBallTrackerProxy::setWholeBodyOn or ALFaceTrackerProxy::setWholeBodyOn).
- head tracking: the two head’s joint are controlled to reach the target. The tracking area is limited by the limits of NAO joints.
- whole body tracking: NAO keeps balance autonomously and adapts his posture to track the target.
Use Cases¶
Here are some possible applications (from the simplest to the more ambitious ones) that can be built from NAO’s ability to track a target.
Case 1: Tracking the red ball using the head: Red Ball Tracker Sample
Case 2: Tracking the red ball using the whole body motion: Tracking a red ball with NAO’s whole body
Case 3: Walk toward a person: Tracking a face using the Walk Tracker box