InitModule_nonFree() - unresolved externel symbol.

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Hi,

I'm writing a small program that extracts descriptors from images and writes them to files.

I'm using (example) detector_descriptor_matcher_evaluation as reference.

I guess this is a very simple problem, but I just can't solve it, I'm probably missing something:

Everything compiled and worked fine (I used FAST and ORB) but I had to use sift so I added a call to cv::initModule_nonfree(); and an include :#include "opencv2/nonfree/nonfree.hpp"

but now I'm getting a linker error:
unresolved external symbol initModule_nonfree(void).

I'm quite sure all the definitions in the project properties are ok since it worked with ORB before I added the call to initModule_nonfree().

Can someone please tell me what I might be missing here and what could be the problem?

Thanks.

Also, another small question: what's the purpose of

saveloadDDM( params_filename, detector, descriptor, matcher );

in the example detector_descriptor_matcher_evaluation ?

here's the code

static void saveloadDDM( const string& params_filename,
                        Ptr<FeatureDetector>& detector,
                        Ptr<DescriptorExtractor>& descriptor,
                        Ptr<DescriptorMatcher>& matcher )
{
    FileStorage fs(params_filename, FileStorage::READ);
    if( fs.isOpened() )
    {
        detector->read(fs["detector"]);
        descriptor->read(fs["descriptor"]);
        matcher->read(fs["matcher"]);
    }
    else
    {
        fs.open(params_filename, FileStorage::WRITE);
        fs << "detector" << "{";
        detector->write(fs);
        fs << "}" << "descriptor" << "{";
        descriptor->write(fs);
        fs << "}" << "matcher" << "{";
        matcher->write(fs);
        fs << "}";
    }
}

I commented it out since it throws and exception. Is it ok not to use it?

Thanks, Gil