how to get depth values and then convert to millimetres in OpenCV with Kinect?
int main( int argc, char* argv[] ){

VideoCapture capture(CV_CAP_OPENNI); // or CV_CAP_OPENNI
for(;;)
{
    Mat depthMap;
    Mat bgrImage;

    capture.grab();

    capture.retrieve( depthMap, CV_CAP_OPENNI_DEPTH_MAP ); // Depth values in mm (CV_16UC1)
    capture.retrieve( bgrImage, CV_CAP_OPENNI_BGR_IMAGE );

    cout << "rows: " << depthMap.rows << " cols: " << depthMap.cols << endl;
    cout << "depth: " << depthMap.at<int>(0,0) << endl;

    imshow("RGB image", bgrImage);

    if( waitKey( 30 ) >= 0 )
        break;
}h
return 0;

rows: 480 cols: 640
depth: 1157
rows: 480 cols: 640
depth: 1157
rows: 480 cols: 640
depth: 1157
rows: 480 cols: 640
depth: 1157

rows: 480 cols: 640
depth: 83690629
rows: 480 cols: 640
depth: 83690629
rows: 480 cols: 640
depth: 83690629
rows: 480 cols: 640
depth: 83690629
rows: 480 cols: 640
depth: 83690629