Feature homography based planar tracking

Example of using features2d framework for interactive video homography matching. ORB features and FLANN matcher are used. The actual tracking is implemented by PlaneTracker class.

Inspired by http://www.youtube.com/watch?v=-ZNYoL8rzPY

Video: http://www.youtube.com/watch?v=FirtmYcC0Vc

Select a textured planar object to track by drawing a box with a mouse.

Sources:

function feature_homography_track_demo(vid)
    % video file, and a default target to track [x,y,w,h]
    win = [];
    if nargin < 1
        vid = fullfile(mexopencv.root(), 'test', 'blais.mp4');
        assert(exist(vid, 'file') == 2, 'Missing video file');
        if true
            win = [135 165 285 175];  % face
        else
            win = [136 0 366 433];    % book
        end
    elseif isempty(vid)
        vid = 0;
    end

    % open video feed, and get first frame
    cap = cv.VideoCapture(vid);
    pause(1);
    assert(cap.isOpened(), 'Failed to open video');
    frame = cap.read();
    assert(~isempty(frame), 'Failed to read frames');

    % prepare plot
    paused = false;
    tframe = zeros(size(frame), class(frame));  % target frame + drawings
    hImg = imshow([frame, tframe]);

    % create and initialize tracker
    tracker = PlaneTracker();
    if ~isempty(win)
        onRect(win);
    end

    % create ROI region selector
    if ~mexopencv.isOctave()
        onHelp();
        roi = RectSelector(hImg);
        roi.clip = true;
        roi.callback = @onRect;
    else
        %HACK: RectSelector not Octave compatible
        %HACK: function handle to nested function not supported in Octave
        roi = struct('isDragging',@()false);
    end

    % listen to keyboard input
    if ~mexopencv.isOctave()
        %HACK: function handle to nested function not supported in Octave
        set(ancestor(hImg,'figure'), 'WindowKeyPressFcn',@onType);
    end

    % main loop
    while ishghandle(hImg)
        playing = ~paused && ~roi.isDragging();
        if playing
            % read new frame
            frame = cap.read();
            if isempty(frame), break; end
        end
        out = [frame, tframe];

        % track and draw keypoints and boundary of target in new frame
        if playing
            tracked = tracker.track(frame);
            if ~isempty(tracked)
                tr = tracked(1);
                out = cv.circle(out, tr.pt1, 2, 'Color',[255 0 0]);
                out = cv.polylines(out, tr.quad, 'Closed',true, ...
                    'Color',[0 255 0], 'Thickness',2);
                % draw matches
                out = cv.line(out, ...
                    bsxfun(@plus, tr.pt0, [size(frame,2) 0]), tr.pt1, ...
                    'Color',[0 0 255]);
            end
        end

        % display result
        set(hImg, 'CData',out);
        if playing
            drawnow;
        else
            pause(0.1);  % slow down a bit if paused
        end
    end
    cap.release();
    if isobject(roi), delete(roi); end

    % --- Callback functions ---

    function onRect(rect)
        %ONRECT  Callback for ROI selector
        %
        %     onRect(rect)
        %
        % ## Input
        % * __rect__ selected rectangle [x,y,w,h], or empty
        %

        if isempty(rect), return; end

        % selection must be made in left image (current frame)
        rect = cv.Rect.intersect(rect, [0 0 size(frame,2) size(frame,1)]);
        if cv.Rect.area(rect) < 1, return; end

        % track new target
        disp('New target...')
        tracker.clear();
        tracker.addTarget(frame, rect);

        % draw keypoints and boundary in target frame
        if ~isempty(tracker.targets)
            t = tracker.targets(1);
            tframe = cv.drawKeypoints(t.image, t.kpts, 'Color',[255 0 0]);
            tframe = cv.rectangle(tframe, t.rect(1:2), t.rect(3:4), ...
                'Color',[0 255 0], 'Thickness',2);
        else
            tframe(:) = 0;
        end

        % un-pause
        paused = false;
    end

    function onType(hfig, e)
        %ONTYPE  Event handler for key press on figure

        switch e.Key
            case {'q', 'escape'}
                close(hfig);

            case 'h'
                onHelp();

            case {'space', 'p'}
                disp('Toggle pause...');
                paused = ~paused;

            case {'c', 'r'}
                disp('Clearing tracker...');
                tracker.clear();
                tframe(:) = 0;
        end
    end

    function onHelp()
        %ONHELP  Display usage help dialog

        h = helpdlg({
            'Select object(s) to track using the mouse.'
            'Hot keys:'
            '  q - quit'
            '  h - help'
            '  p - pause'
            '  c - clear targets'
        });

        % wait for user to accept dialog
        set(h, 'WindowStyle','modal');
        waitfor(h);
    end
end

New target...