VisionWorks Toolkit Reference

September 29, 2015 | 1.0 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 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:

                                 (frame)
                                    |
                             [ColorConvert]
                                    |
                +-------------------+-------------------+
                |                                       |
        [GaussianPyramid]                         [HarrisTrack]
                |                                       |
        (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.

The NVIDIA extended Harris Corner function divides the image into cells of the same size and looks for corners independently in each cell. In this way, corners are uniformly detected across the image. These corners are the keypoints that are tracked in the next frames.

                                    (frame)
                                       |
                                [ColorConvert]
                                       |
                               [ChannelExtract]
                                       |
                               [GaussianPyramid]
                                       |
(previous pyramid)             (current pyramid)         (points to track in the previous frame)
        |                              |                                      |
        +------------------------------+--------------------------------------+
                                       |
                              [OpticalFlowPyrLK]
                                       |
                               (tracked points)
                                       |
                                 [HarrisTrack]
                                       |
                     (points to track in the next frame)
Note
Current implementation of Harris corner detector supports input frames only with total number of pixels less than \(2^{20}\).

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
On Vibrante V3Le, V4L platforms hardware accelerated video playback is supported for H.264 elementary streams only.
The V4L platform has a permissions issue. If input data are an H.264 elementary stream, hardware decoder is used and sample must be executed with super user permissions, i.e., with sudo.

-c, --config

-m, --mask

-h, --help

Operational Keys