VisionWorks Toolkit Reference

December 18, 2015 | 1.2 Release

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Feature Tracker Demo App

Feature Tracker Demo user guide.

Introduction

nvx_demo_feature_tracker is a simple local feature tracking demo that uses the Harris or FAST feature detector to get the initial list of features and tracks them using the sparse pyramidal optical flow method (Lucas-Kanade).

In the first frame, Gaussian pyramid is created and initial points are detected so that the features can be found quickly at low resolution and can also be located more accurately as you go down the pyramid.

The initial points are detected using Harris Corner detector. The NVIDIA extended Harris and FAST Corner functions divide the image into cells of the same size and look for corners independently in each cell. This way, corners are uniformly detected across the image. These corners are the keypoints that are tracked in the next frames.

                                 (frame)
                                    |
                             [ColorConvert]
                                    |
                +-------------------+-------------------+
                |                                       |
        [GaussianPyramid]                         [CornerTrack]
                |                                       |
        (initial pyramid)                        (initial points)

In subsequent frames, points are tracked with the Lucas-Kanade method between two pyramid images. Then, corner detection is performed to restore lost points.

                                    (frame)
                                       |
                                [ColorConvert]
                                       |
                               [ChannelExtract]
                                       |
                               [GaussianPyramid]
                                       |
(previous pyramid)             (current pyramid)         (points to track in the previous frame)
        |                              |                                      |
        +------------------------------+--------------------------------------+
                                       |
                              [OpticalFlowPyrLK]
                                       |
                               (tracked points)
                                       |
                                 [CornerTrack]
                                       |
                     (points to track in the next frame)
Note
In the figure above, the entities inside () denote data and the entities inside [] denote the vision functions.
Current implementation of Harris and FAST corner detectors supports input frames only with total number of pixels less than \(2^{32}\).

Installation and Usage

nvx_demo_feature_tracker is installed in the following directory:

/usr/share/visionworks/sources/demos/feature_tracker

For the steps to build sample applications, see the Sample and Demos User Guides section for your OS.

Executing the Feature Tracker Demo

./nvx_demo_feature_tracker [options]

Command Line Options

This topic provides a list of supported options and the values they consume.

-s, --source

Note
The V4L platform has a permissions issue. The hardware decoder is used and the sample must be executed with super user permissions, i.e., with sudo.

-c, --config

-m, --mask

-h, --help

Operational Keys