armadillo to other data format conversion

Armadillo is a C++ linear algebra library, especially for computer vision application.

Armadillo is more similar to MATLAB with decent performance. (check http://nghiaho.com/?p=1726 for comparison).

We may want to cooperate Armadillo with OpenCV, STL or FFTW. In this blog the conversion between STL and OpenCV will be described.

1. armadillo to STL vector

2. Armadillo to OpenCV, Since OpenCV data is saved in row-wised, and armadillo data is saved in column-wised, therefore, when we convert the data, we may need to do transformation at first. The following is the sample code.

3. OpenCV to Armadillo

4. STL 2D vector (vector<vector<T> >) to Opencv cv::Mat 2D matrix
Hope these could be helpful for some one is seeking the answer~~

Read ViPer data into MATLAB

ViPer as a ground truth labeling software and protocol has been widely used in computer vision community, such as UCF Youtube dataset. However, since the ground truth information has been stored in XML format, for those who are not familiar with XML and using MATLAB for experiments, this protocol may raise some difficulty.

This blog will give an example of how to read the XML ground truth information into MATLAB.

The example xml file will be the 'v_biking_13_05.xgtf' from UCF Youtube dat set, with bounding box annotation (http://www.cs.ucf.edu/~liujg/YouTube_Action_dataset.html).

1.  download viper-gt.jar from http://viper-toolkit.sourceforge.net, click ViPER Light Distribution (Recommended) [May 25, 2005] under Software section.

In MATLAB type in the following command
>> javaaddpath(' ViPER_Folder/viper-gt.jar')

2. Type in the following commands to obtain an viper object, replace the filename as your v_biking_13_05.xgtf with the path.

>> docBuilder = DocumentBuilderFactory.newInstance();

>> docBuilder.setNamespaceAware(true);

>> docElement = docBuilder.newDocumentBuilder().parse(filename).getDocumentElement();

>> parser = viper.api.impl.ViperParser;

>> objviper = parser.parseDoc(docElement);

3. Obtain a string of bounding box information: (The getChild() may vary depend on different xgtf files, but at least for this example file it works)

str = char(objviper.getChild(1).getChild(0).getChild(1).getAttribute('Location').toString);

4. parse this str as a n x 4 matrix containing BoundingBox Information
The following code should be able to help you to do this job.

function BB = parseStr(str)

dq = strfind(str, '"'); % double quote locations

bn = strfind(str, ')'); % brace number

if ( length(dq) / 2 ~= length(bn) )

    error('dq should be equal to 2 * bn');

end

BB = [];

for i = 1 : length(bn)

    tmpBB = parseOneSeg(str( dq( (i-1) * 2 + 1) + 1 : bn(i) - 1) );

    BB = cat(1, BB, tmpBB);

end

end

function tmpBB = parseOneSeg(str)

dq = strfind(str, '"');

BB = parseBB(str(1 : dq - 1) );

strNum = str2num( str( strfind(str, '[') + 1 : strfind(str, ',') - 1) );

endNum = str2num( str( strfind(str, ', ') + 2 : length(str) ) );

tmpBB = repmat(BB, endNum - strNum, 1);

end

function BB = parseBB(str)

BB = zeros(1, 4);

sp = strfind(str, ' '); % space location

sp = [0 sp length(str)+1];

for i = 1 : 4

    BB(i) = str2num( str( sp(i)+1 : sp(i+1) - 1) );

end

end

5. Last you may want to visualize the bounding box
The following small script may help you to do that.

function readViper_visualize(BB, videoName)

video = VideoReader(videoName);

nFrame = video.NumberOfFrames;

nRow = size(BB, 1);

n = min(nFrame, nRow);

% BB = BB(:, [3 4 1 2]);

for i = 1 : n

    I = read(video, i);

    imshow(I);

    rectangle('Position', BB(i, :), 'EdgeColor', 'r', 'LineWidth', 3);

    title(['Frame ' num2str(i)]);

end