How to set parameters for Orb in Java?

edit

This previous answer seems clear, except the following code doesn't change the number of features detected. How to extract more than 500 features (the default)? The parameter list / order was changed to match the protected variable list in orb.cpp.

File outputFile = new File("detectorParams.yml");
detector = FeatureDetector.create(FeatureDetector.ORB);
detector.read(outputFile.getAbsolutePath());
MatOfKeyPoint kp1 = new MatOfKeyPoint();
for (images in video) {
  Mat img = ...
  detector.detect(img, kp1);
}

YML Parameter file:

%YAML:1.0
nfeatures: 2000
scaleFactor: 1.2000000000000000e+000
nlevels: 8
edgeThreshold: 31
firstLevel: 0
wta_k: 2
scoreType: 0
patchSize: 31
fastThreshold: 0

Here is the xml file that was tried (generated based on this example

<?xml version="1.0"?>
<opencv_storage>
<nfeatures>2000</nfeatures>
<scaleFactor>1.2000000000000000e+000</scaleFactor>
<nlevels>8</nlevels>
<edgeThreshold>31</edgeThreshold>
<firstLevel>0</firstLevel>
<wta_k>2</wta_k>
<scoreType>0</scoreType>
<patchSize>31</patchSize>
<fastThreshold>0</fastThreshold>
</opencv_storage>

kp1 always has 500 rows which is the default value for nfeatures. So, the reading the yml file did not change the value of nfeatures to 2000. I have tried 1) the original list in the previous answer, 2) writing to xml and yml but I didn't change the format for xml, 3) writing only nfeatures.

Code to generate xml / yml files

#include "opencv2/opencv.hpp"
#include <time.h>

using namespace cv;

int main(int, char** argv)
{
    int nfeatures=2000, nlevels=8, edgeThreshold=31, firstLevel=0, wta_k=2,
            scoreType=ORB::HARRIS_SCORE, patchSize=31, fastThreshold=0;
    double scaleFactor=1.2;

    for (int ft=0; ft<2; ft++) {
        FileStorage fs;
        if (ft==0) {
            fs = FileStorage("test_descrip.xml", FileStorage::WRITE);
        } else {
            fs = FileStorage("test_descrip.yml", FileStorage::WRITE);
        }
        fs << "nfeatures" << nfeatures;
        fs << "scaleFactor" << scaleFactor;
        fs << "nlevels" << nlevels;
        fs << "edgeThreshold" << edgeThreshold;
        fs << "firstLevel" << firstLevel;
        fs << "wta_k" << wta_k;
        fs << "scoreType" << scoreType;
        fs << "patchSize" << patchSize;
        fs << "fastThreshold" << fastThreshold;
        fs.release();
    }

    return 0;
}

I tried writing a c++ to output the parameters, but nothing gets printed.

int main(int argc, char** argv) {

//    CV_WRAP static Ptr<ORB> create(int nfeatures=500, float scaleFactor=1.2f, int nlevels=8, int edgeThreshold=31,
//        int firstLevel=0, int WTA_K=2, int scoreType=ORB::HARRIS_SCORE, int patchSize=31, int fastThreshold=20);
    Ptr<ORB> orb=ORB::create(2000,1.3f,9,32,0,2,ORB::HARRIS_SCORE,35,22);

    FileStorage fs1("testorb.yml", FileStorage::WRITE);
    FileStorage fs2("testorb.xml", FileStorage::WRITE);
    orb->setMaxFeatures(2500);
    orb->write(fs1);
    orb->write(fs2);
    return 0;
}

This creates the two files but they are both empty

testorb.xml

<?xml version="1.0"?>
<opencv_storage>
</opencv_storage>

testorb.yml

%YAML:1.0