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For some reasons I need to filter out rows of a Mat. (I need to filter out some descriptors of ORB)

Which way do you suggest me? I haven't find any method to remove a single row from a Mat. So I was thinking I could iteratively inserting the good rows in a new Mat.

C++ pseudocode (with removing):

Mat desc;
ORB(myImage,cv::noArray,kp,desc);
matcher->match( myPreviousDesc, desc, matches );

for(auto i=0;i<matches.size();i++) {
   if (some conditions) {
      Remove the ith row of desc:
      erase( desc.row( matches[i].queryIdx ) ); // pseudo
   }
}

How would you erase a single row from a Mat after checking for some conditions (or adding only the selected row in a new Mat) ?

Or how to add a new row iteratively to a new Mat ?

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1 Answer

up vote 3 down vote accepted

Iteratively adding a new row is straightforward with cv::Mat::push_back().

Adding only good descriptors might look like this:

cv::Mat good_descriptors;   
for (auto i = 0; i < matches.size(); ++i)
{
    if (/*something*/)
    {
        cv::Mat row = desc.row(matches[i].queryIdx);
        good_descriptors.push_back(row);
    }
}
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answers.opencv.org/question/13871/… I think you don't need to create that additional variable row, also don't forgot taht you need a final reshape. +1 anyway – yes123 May 24 at 19:27
Explicitly declaring row isn't strictly necessary. I did it for readability. And reshape() isn't necessary unless you want to be extra sure--the original number of columns is preserved. – Aurelius May 24 at 20:31
Hm, acutally I think you are right. Without reshape code is working normally – yes123 May 25 at 13:42

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