从 QT 资源加载 openCV Haarcascade

Question

I want to add the openCV cascades to the ressource managment of QT. But i'm failed.

I've tested this code:

// load cascades
QUrl *location_cascade= new QUrl("qrc:/cascades/haarcascade_frontalface_alt.xml");
std::string file=location_cascade->toString().toStdString();
CvHaarClassifierCascade* cascade = (CvHaarClassifierCascade*)cvLoad( file);

But than the compiler said:

cannot convert 'std::string* {aka std::basic_string<char>*}' to 'const char*' for argument '1' to 'void* cvLoad(const char*, CvMemStorage*, const char*, const char**)'

Has someone an idea?

Update Currently the file is in the source folder of the project. Can i access this file by relative path? maybe by a constant that points to the src.dir?

greetings

Answer 1

Compiler tells you that first argument of cvLoad should be const char* , but you are passing std::string . You need to call it like cvLoad(file.c_str()) .

But even if you manage to compile that code it will probably not work, as openCV knows nothing about Qt resources and won't be able to open the file with that name.

Answer 2

Even so, this question is 2 years old, I want to share the workaround I used.

QString sPath = QCoreApplication::applicationDirPath().append("/frontalface.xml")
QFile::copy(":/android-sources/OpenCV/haarcascade_frontalface_default.xml" , sPath);
cv::CascadeClassifier faceCascade = cv::CascadeClassifier(sPath.toStdString());
QFile::remove(sPath);

It works, but you have to go the detour over the local harddrive. Still usefull for android applications.

Answer 3

using namespace cv;    
QFile xmlRes(":/new/cascades/res/cascade.xml");
    if (xmlRes.open(QIODevice::ReadOnly)) {
        QString data(xmlRes.readAll());
        FileStorage fs(data.toStdString().c_str(), FileStorage::MEMORY | FileStorage::FORMAT_XML);
        if (!cascade.read(fs["cascade"]))
            qDebug() << "ERROR: Could not read classifier cascade.";
    }