How would I publish a 2D float Array through a ROS message?

edit

I am currently working on a circle detection app. Using OpenCV, I get a std::vector<std::vector<float>> named v. Now I want to send this to a different executable node. So I made a simple Circles.msg which is:

float32[][] circles

However, I get a bunch of errors, mostly which are:

'const class std::vector<std::vector<float> >' has no member named '__getMD5Sum'

From the line:

circle_pub_.publish(v);

which I get from:

ros::Publisher circle_pub_;
circle_pub_ = node.advertise("/circles", 1);

So therefore, I don't know how to approach this problem.

I also do not understand how to subscribe to this topic. Currently I got:

circles_in = node.subscribe("/circles", 1, organizer_callback);
void organizer_callback( const std::vector< std::vector<float> >& circles) {
    ....
}

Is this okay? Please let me know if you know any more information!

The Code

Here is the most important parts of my program as of now:

class ImageConverter {
  ros::NodeHandle nh_;
  image_transport::ImageTransport it_;
  image_transport::Subscriber image_sub_;
  image_transport::Publisher image_pub_;
  ros::Publisher circle_pub_;

public:
  ImageConverter()
    : it_(nh_)
  {

        // Subscribe to the Bottom Raw Image
        image_sub_ = it_.subscribe("/ardrone/bottom/image_raw", 1, 
                &ImageConverter::imageCb, this);


        // Advertisng the Circles being detected from this 
                circle_pub_ =  nh_.advertise<zlab_drone::Circles>("/circles", 1);

  }

  void imageCb(const sensor_msgs::ImageConstPtr& msg)
  {
       // Find the circles from a particular video  
       cv::vector<cv::Vec3f> circles; 
       cv::HoughCircles(img_bin, circles, CV_HOUGH_GRADIENT, 1, 70, 140, 15, 
                    20, 400);


       std::vector<zlab_drone::Circle> v;

       for(int i = 0; i < circles.size(); ++i) {
           const cv::Vec3f& c = circles[i];
           v[i][0] = c[0];
           v[i][1] = c[1];
           v[i][2] = c[2];
       } 

       circle_pub_.publish(v);

    }
};

Subscriber

Here's the code from my subscriber:

// Gathering Data from the messages
for (std::vector<zlab_drone::Circles>::const_iterator gp = 
    msg->circles.begin(); gp!= msg->circles.end(), ++gp) {
    for (std::vector<float>::const_iterator dp = 
        gp->circle.begin(); dp != gp->circle.end(); ++dp) {
        circles[gp][dp] = gp->circle(dp); 
    }
}