Dimension reduction with PCA in OpenCV

I have a 3xN Mat data, which is saved in yaml file and looks like:

%YAML:1.0

data1: !!opencv-matrix
rows: 50
 cols: 3
 dt: d
 data: [ 7.1709999084472656e+01, -2.5729999542236328e+01,
   -1.4074000549316406e+02, 7.1680000305175781e+01,
   -2.5729999542236328e+01, -1.4075000000000000e+02,
   7.1639999389648438e+01, -2.5729999542236328e+01,
   -1.4075000000000000e+02, 7.1680000305175781e+01,
   -2.5729999542236328e+01, -1.4075000000000000e+02, ...

I want to reduce the dimension of my 3D data to 1D or rather 2D and after that visualize it on a QwtPlotCurve. In order to do that, I have implemented pca function under opencv, but have no idea how to get the calculated x and y coordinates from pca result:

int numOfComponents= 100;
PCA pca(data, cv::Mat(), CV_PCA_DATA_AS_ROW, numOfComponents);

Mat mean= pca.mean.clone();
Mat eigenvalues= pca.eigenvalues.clone();
Mat eigenvectors= pca.eigenvectors.clone();