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2013-02-27 19:05:24 -0500 commented answer syntax for particle filter in opencv 2.4.3

It probably was moved because it didn't work. This works and it's an important and useful algorithm.

2013-02-26 09:06:09 -0500 asked a question Fill a matrix

What is the easiest way to fill a cv::Mat object with scalars of a single value?

2013-02-21 17:59:52 -0500 answered a question syntax for particle filter in opencv 2.4.3

The cvConDensation code had some bugs in its resampling stage and did not work very well. (Neither did the example in the OpenCV book.) Here is an example that works. Note that the DynamMatr matrix is not automatically initialized, so you have to do that yourself.

// Example of how to use the OpenCV Particle Filter.
// 
// Stolen largely from morethantechnical.com's nice mouse_kalman project.
//

#include <iostream>
#include <vector>

#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/video/tracking.hpp>
#include <opencv2/legacy/legacy.hpp>

using namespace std;

#define drawCross( center, color, d )                  \
  line( img, cv::Point( center.x - d, center.y - d ),           \
    cv::Point( center.x + d, center.y + d ), color, 2, CV_AA, 0);   \
  line( img, cv::Point( center.x + d, center.y - d ),           \
    cv::Point( center.x - d, center.y + d ), color, 2, CV_AA, 0 )

struct mouse_info_struct { int x,y; };
struct mouse_info_struct mouse_info = {-1,-1}, last_mouse;

vector<cv::Point> mouseV, particleV;
int counter = -1;

// Define this to proceed one click at a time.
//#define CLICK 1
#define PLOT_PARTICLES 1

void on_mouse(int event, int x, int y, int flags, void* param) {
#ifdef CLICK
  if (event == CV_EVENT_LBUTTONUP) 
#endif
  {
    last_mouse = mouse_info;
    mouse_info.x = x;
    mouse_info.y = y;
    counter = 0;
  }
}

int main (int argc, char * const argv[]) {
  cv::Mat img(650, 650, CV_8UC3);
  char code = (char)-1;

  cv::namedWindow("mouse particle");
  cv::setMouseCallback("mouse particle", on_mouse, 0);

  cv::Mat_<float> measurement(2,1); 
  measurement.setTo(cv::Scalar(0));

  int dim = 2;
  int nParticles = 25;
  float xRange = 650.0;
  float yRange = 650.0;

  float minRange[] = { 0, 0 };
  float maxRange[] = { xRange, yRange };
  CvMat LB, UB;
  cvInitMatHeader(&LB, 2, 1, CV_32FC1, minRange);
  cvInitMatHeader(&UB, 2, 1, CV_32FC1, maxRange);

  CvConDensation* condens = cvCreateConDensation(dim, dim, nParticles);

  cvConDensInitSampleSet(condens, &LB, &UB);

  // The OpenCV documentation doesn't tell you to initialize this
  // transition matrix, but you have to do it.  For this 2D example, 
  // we're just using a 2x2 identity matrix.  I'm sure there's a slicker 
  // way to do this, left as an exercise for the reader.
  condens->DynamMatr[0] = 1.0;
  condens->DynamMatr[1] = 0.0;
  condens->DynamMatr[2] = 0.0;
  condens->DynamMatr[3] = 1.0;

  for(;;) {

    if (mouse_info.x < 0 || mouse_info.y < 0) {
      imshow("mouse particle", img);
      cv::waitKey(30);
      continue;
    }

    mouseV.clear();
    particleV.clear();

    for(;;) {
      code = (char)cv::waitKey(100);

      if( code > 0 )
    break;

#ifdef CLICK
      if (counter++ > 0) {
    continue;
      } 
#endif

      measurement(0) = mouse_info.x;
      measurement(1) = mouse_info.y;

      cv::Point measPt(measurement(0),measurement(1));
      mouseV.push_back(measPt);

      // Clear screen
      img = cv::Scalar::all(100);

      for (int i = 0; i < condens->SamplesNum; i++) {

    float diffX = (measurement(0) - condens->flSamples[i][0])/xRange;
    float diffY = (measurement(1) - condens->flSamples[i][1])/yRange;

    condens->flConfidence[i] = 1.0 / (sqrt(diffX * diffX + diffY * diffY));

    // plot particles
#ifdef PLOT_PARTICLES
    cv::Point partPt(condens->flSamples[i][0], condens->flSamples[i][1]);
    drawCross(partPt , cv::Scalar(255,0,255), 2);
#endif

      }

      cvConDensUpdateByTime(condens);

      cv::Point statePt(condens->State[0], condens->State[1]);
      particleV.push_back(statePt);

      // plot points
      drawCross( statePt, cv::Scalar(255,255,255), 5 ...
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