Custom type for cv :: Mat in OpenCV

Question

Custom type for cv :: Mat in OpenCV

I want to create an array using cv :: Mat with my custom type. Here is my code:

typedef struct{
  int x;
  int y;
  float prob;
}CellXY;

void main(){

  cv::Mat_<CellXY> map(10, 10);

  std::cout << "Width = " << map.cols << ", Height = " << map.rows << std::endl;
  std::cout << "### Assignment ###" << std::endl;
  for (int j=0; j<map.rows; j++){
    for (int i=0; i<map.cols; i++){
      map.at<CellXY>(j, i).x = i;
      map.at<CellXY>(j, i).y = j;
      map.at<CellXY>(j, i).prob = (float)(i + j * map.cols);

      std::cout << map.at<CellXY>(j, i).prob 
        << " (" << map.at<CellXY>(j, i).x
        << "," << map.at<CellXY>(j, i).y
        << ")\t";
    }
    std::cout << std::endl;
  }

  std::cout << "### Display ###" << std::endl;
  for (int j=0; j<map.rows; j++){
    for (int i=0; i<map.cols; i++){
      std::cout << map.at<CellXY>(j, i).prob 
        << " (" << map.at<CellXY>(j, i).x
        << "," << map.at<CellXY>(j, i).y
        << ")\t";
    }
    std::cout << std::endl; 
  }
  map.release();
}

However, the results between the Purpose and Display sections do not match:

How do you make these results the same?

+3

c ++ opencv

puwanan 29 Mar 17 at 9:11 am

source to share

1 answer

Miki · Accepted Answer · 2017-03-29T09:56:26+0000

This is because OpenCV doesn't know DataType

your class. For this you need a specialization, for example:

typedef struct {
    int x;
    int y;
    float prob;
}CellXY;


// Add this!!!!!!
namespace cv {
template<> class DataType<CellXY>
{
public:
    typedef CellXY      value_type;
    typedef value_type  work_type;
    typedef value_type  channel_type;
    typedef value_type  vec_type;
    enum { generic_type = 0,
        depth        = CV_32F, // Might cause problems... I'm saying it all made of floats (and not 2 int a 1 float)
        channels     = 3,
        fmt          = (int)'p',
        type         = CV_MAKETYPE(depth, channels)
    };
};
}

void main() {
    ...
}

But in general, I think it's best to avoid messing with these implementation details and just use a better data structure. Recommendation: use Mat

only for primitive types . In fact, you cannot use it in other OpenCV functions ...

Here are some ways to solve your problem:

Use a different data structure: eg. a std::vector<std::vector<CellXY>>

or "expanded"std::vector<CellXY>

Make a class CellXYMatrix

that deals with storage CellXY

:

class CellXYMatrix
{
     std::vector<CellXY> _mat; // your matrix of CellXY
     int _r; // rows
     int _c; // cols

public:
     CellXYMatrix(int rows, int cols) : _r(rows), _c(cols), _mat(rows * cols) {};

     void set(int row, int col, const CellXY& cell) {
        _mat[row * _c + col] = cell;
     }
     CellXY& get(int row, int col) {
        return _mat[row * _c + col];
     }  
}

You can eventually overload operator()

to make access similar to OpenCV masks.

If the fields x

and y

in CellXY

are relative to the position of the matrix, why do you need them? You can just have Mat1f

(aka Mat_<float>

) for your probabilities and x, y is the position in the matrix.

Custom type for cv :: Mat in OpenCV

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