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How to read a Matrix from a child node with FileStorage API

asked 2015-07-12 10:48:00 -0500

valentine gravatar image

updated 2015-08-25 17:21:04 -0500

Hello guys,

I am having a little issue here. I saved a couple of mat as child nodes in xml using the Filestorage API in opencv. However when i try to read them back the filestorage API reads the same values which are wrong for all the Matrices in the xml file. I don't know where am getting it wrong. please help.

Here is my code for writing and reading.

FileStorage file(filename, FileStorage::WRITE);
file << "Features" << "{";
for (int i = 0; i < TrainFeatureVector.size(); i++){
  string element1 = "f" + to_string(i);
  file << element1 << TrainFeatureVector[i];
}
file << "}"

FileStorage fs(filename, FileStorage::READ);
Mat feat;
string element;
string element1;
FileNode k = fs["Features"];
for (int i = 0; i < k.size(); i++){
 element1 = "f" + to_string(i);
 k[element1] >> feat;
 Fvector.push_back(feat);}

Here is my xml file C:\fakepath\sxml.png

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Comments

May be you should try something like k=fs["f0"] or k=fs["f1"]

LBerger gravatar imageLBerger ( 2015-07-12 11:07:53 -0500 )edit

Tried using FileNodeIterator but only returns one Matrix. Please need help on this.

valentine gravatar imagevalentine ( 2015-07-12 12:15:27 -0500 )edit

TrainFeatureVector is a vector<mat> ?

berak gravatar imageberak ( 2015-07-13 00:08:44 -0500 )edit

@berak, yes

valentine gravatar imagevalentine ( 2015-07-14 12:12:50 -0500 )edit

3 answers

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answered 2015-07-16 12:13:54 -0500

valentine gravatar image

Hello everyone.

Here is what i did to resolve this issue.

void readfeaturesFileNodeList(const FileNode& fn, vector<Mat>& result, int i){
    string element1;
    Mat feat;
    for (FileNodeIterator current = fn.begin(); current != fn.end();current++){
        element1 = "f" + to_string(i);
        FileNode rt = *current;
        rt[element1]>> feat;
        result.push_back(feat);
    }
}

and the second function is given below.

void ReadGlobalFeatures(string filename,vector<Mat>& Fvector){
    FileStorage fs(filename, FileStorage::READ);
    Mat feat;
    vector<Mat> vfeat;
    string element;
    string element1;
    FileNode k = fs.root();

    for (int i = 0; i <TrainLabels.size(); i++){
        //element1 = "f" + to_string(i);
        FileNode tempID = k;
        readfeaturesFileNodeList(tempID, vfeat,i);
    }
    Fvector = vfeat;
    fs.release();
}

Thanks berak and all who contributed to this i am really grateful. This is truly the best opencv forum and i have learnt from all you.

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answered 2015-07-12 12:31:31 -0500

LBerger gravatar image

updated 2015-07-12 12:43:15 -0500

Ok i was wrong I have looked in my code and I have found :

cv::FileNode op = node;
nomOperation=(string)op["op"];
nbOperande= op["nbOperande"];
indOpFenetre.resize(nbOperande);
this->op.resize(nbOperande);
indRes = (int)op["res"];
indEtape = (int)op["indEtape"];
idOperation = (int)op["idOperation"];
nomSequence = (string)op["nomSequence"];
cv::FileNode opl = op["intParam"];
cv::FileNodeIterator it = opl.begin(), it_end = opl.end();
for (; it != it_end; ++it)
 {
   intParam[(string)(*it)["nom"]] = DomaineParametreOp<int>((*it)["valeur"], (*it)["minVal"], (*it)["maxVal"], (*it)["pasVal"]);;
}

for file like this

image description

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answered 2015-07-14 12:35:09 -0500

berak gravatar image

maybe it gets easier, if you just write/read a vector/list of Mat's, and don't try to make it a 'dictionary'. your f1,f2,f3 keys are quite artificial here.

vector<Mat> TrainFeatureVector(4,Mat::eye(4,4,CV_32F)); // just for demo purpose
FileStorage fsw("ma.xml", FileStorage::WRITE);
fsw << "Features" << "[";
for (int i = 0; i < TrainFeatureVector.size(); i++)
{
    fsw << TrainFeatureVector[i];
}
fsw << "]";
fsw.release();


vector<Mat> TrainFeatureVector2;
FileStorage fsr("ma.xml", FileStorage::READ);
FileNode k = fsr["Features"];
for (FileNodeIterator it=k.begin(); it!=k.end(); ++it)
{
    Mat feature;
    (*it) >> feature;
    TrainFeatureVector2.push_back(feature);
}
cerr << TrainFeatureVector2[2];

[1, 0, 0, 0;
 0, 1, 0, 0;
 0, 0, 1, 0;
 0, 0, 0, 1]

 <?xml version="1.0"?>
<opencv_storage>
<Features>
  <_ type_id="opencv-matrix">
    <rows>4</rows>
    <cols>4</cols>
    <dt>f</dt>
    <data>
      1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1.</data></_>
  <_ type_id="opencv-matrix">
    <rows>4</rows>
    <cols>4</cols>
    <dt>f</dt>
    <data>
      1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1.</data></_>
  <_ type_id="opencv-matrix">
    <rows>4</rows>
    <cols>4</cols>
    <dt>f</dt>
    <data>
      1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1.</data></_>
  <_ type_id="opencv-matrix">
    <rows>4</rows>
    <cols>4</cols>
    <dt>f</dt>
    <data>
      1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1.</data></_></Features>
</opencv_storage>
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Comments

Dear berak,

Thanks for answer. done exactly this but its reading wrong values. The values am getting its wat in xml file

valentine gravatar imagevalentine ( 2015-07-14 15:40:57 -0500 )edit
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Asked: 2015-07-12 10:48:00 -0500

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Last updated: Jul 16 '15