Accessing a returned value from openCV function C++ NDK

Question

I am using the Knn findNearest function in OpenCV, which takes in the following parameters:

Mat response;
Mat dist;

knn->findNearest(testFeature, K, noArray(), response, dist);

The output returned from response and dist is of type OutputArray.

How do I access the results of response and dist in this format? Ideally I would like to convert to Mat int.

you can put mat data into cpp array and then send it via jni array — hariprasad, Dec 28 '17 at 04:38
How do I do this? I can't find any documentation for putting an OutputArray into a cpp array — Ber12345, Dec 28 '17 at 09:45
https://stackoverflow.com/questions/1610045/how-to-return-an-array-from-jni-to-java. this may helps — hariprasad, Dec 28 '17 at 09:58
This doesn't help I'm afraid. Would you be able to give an example of what you said to do in your first answer? How do I get the mat data into a cpp array? — Ber12345, Dec 28 '17 at 12:57

score 0 · Answer 1 · answered Dec 29 '17 at 06:26

If you want to copy the mat data into cpp array you can do like this. I assume the Mat data you want to return is of float type.

int size=response.rows*response.cols*resonse.channels();
float* outArr=new float[size];
std::memcpy(outArr,response.data,size*sizeof(float));

you need to delete outArr after copying it to JNIArray.

1 Answers1