# Publishing Velocity of Kalman Filtered Clusters

Hello everyone, I've segmented an incoming Point Cloud, applied an euclidian cluster extraction and then associated the data between frames combined with a Kalman filter.

Right now I'm publishing text markers above every object, containing the object id, x and y position. I wanna publish the x and y velocity ( from the Kalman filter) aswell , but I'm struggling to find out how. In Line 780 - 785 I've tried to so so with a geometry:msgs::Twist Publisher, but it doesn't publish anything.

I would appreciate any suggestion and thank you in advance!

```
using namespace std;
using namespace cv;
std::string stringify(float value)
{
std::ostringstream oss;
oss << value;
return oss.str();
}
ros::Publisher objID_pub;
// KF init
int stateDim=4;// [x,y,v_x,v_y]//,w,h]
int measDim=2;// [z_x,z_y,z_w,z_h]
int ctrlDim=0;
cv::KalmanFilter KF0(stateDim,measDim,ctrlDim,CV_32F);
cv::KalmanFilter KF1(stateDim,measDim,ctrlDim,CV_32F);
cv::KalmanFilter KF2(stateDim,measDim,ctrlDim,CV_32F);
cv::KalmanFilter KF3(stateDim,measDim,ctrlDim,CV_32F);
cv::KalmanFilter KF4(stateDim,measDim,ctrlDim,CV_32F);
cv::KalmanFilter KF5(stateDim,measDim,ctrlDim,CV_32F);
ros::Publisher pub_cluster0;
ros::Publisher pub_cluster1;
ros::Publisher pub_cluster2;
ros::Publisher pub_cluster3;
ros::Publisher pub_cluster4;
ros::Publisher pub_cluster5;
ros::Publisher objState0;
ros::Publisher objState1;
ros::Publisher objState2;
ros::Publisher objState3;
ros::Publisher objState4;
ros::Publisher objState5;
ros::Publisher markerPub;
ros::Publisher textPub;
std::vector<geometry_msgs::Point> prevClusterCenters;
cv::Mat state(stateDim,1,CV_32F);
cv::Mat_<float> measurement(2,1);
std::vector<int> objID;// Output of the data association using KF
// measurement.setTo(Scalar(0));
bool firstFrame=true;
// calculate euclidean distance of two points
double euclidean_distance(geometry_msgs::Point& p1, geometry_msgs::Point& p2)
{
return sqrt((p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y) + (p1.z - p2.z) * (p1.z - p2.z));
}
/*
//Count unique object IDs. just to make sure same ID has not been assigned to two KF_Trackers.
int countIDs(vector<int> v)
{
transform(v.begin(), v.end(), v.begin(), abs); // O(n) where n = distance(v.end(), v.begin())
sort(v.begin(), v.end()); // Average case O(n log n), worst case O(n^2) (usually implemented as quicksort.
// To guarantee worst case O(n log n) replace with make_heap, then sort_heap.
// Unique will take a sorted range, and move things around to get duplicated
// items to the back and returns an iterator to the end of the unique section of the range
auto unique_end = unique(v.begin(), v.end()); // Again n comparisons
return distance(unique_end, v.begin()); // Constant time for random access iterators (like vector's)
}
*/
/*
objID: vector containing the IDs of the clusters that should be associated with each KF_Tracker
objID[0] corresponds to KFT0, objID[1] corresponds to KFT1 etc.
*/
std::pair<int,int> findIndexOfMin(std::vector<std::vector<float> > distMat)
{
cout<<"findIndexOfMin cALLED\n";
std::pair<int,int>minIndex;
float minEl=std::numeric_limits<float>::max();
cout<<"minEl="<<minEl<<"\n";
for (int i=0; i<distMat.size();i++)
for(int j=0;j<distMat.at(0).size();j ...
```

( My current guess is something with KF0.statePost, to retrieve the velocity, and then somehow publish it, but im not exactly sure)

Ive actually managed to publish something:

0 and 1 give me the correct x and y value, but 2 and 3 give me a velocity, which is something around 10^-6, which is too low