How to get the coordinate of feature points of popsift::FeaturesDev?

[BruceXSK]

I want to get the coordinate of feature points after match. So I add cout << lFeatures->getFeatures()[0].xpos << endl; to src/application/match.cpp. Then the program broke. It shows Segmentation fault (core dumped).
But I did the same thing to src/application/main.cpp, added cout << feature_list->_ext[0].xpos << endl; to void read_job( SiftJob* job, bool really_write ), it worked well.
I noticed that the class of lFeatures is popsift::FeaturesDev, and the feature_list's is popsift::Features. So why I cannot get the infomation of feature from popsift::FeaturesDev? What should I do? THANKS!

[griwodz]

The FeaturesDev memory exists only in GPU memory, not in the CPU memory. To use the coordinates in the CPU after matching, you must transfer them first.

You could do something like this:

    FeaturesHost* features = new FeaturesHost( lFeatures->getFeatureCount(), lFeatures->getDescriptorCount() );
    features->pin( );
    cudaMemcpy( features->getFeatures(),
                             lFeatures->getFeatures();
                             lFeatures->getFeatureCount() * sizeof(Feature),
                             cudaMemcpyDeviceToHost );
    cudaMemcpy( features->getDescriptors(),
                             lFeatures->getDescriptors(),
                             lFeatures->getDescriptorCount() * sizeof(Descriptor),
                             cudaMemcpyDeviceToHost );
    features->unpin( );

[BruceXSK]

The FeaturesDev memory exists only in GPU memory, not in the CPU memory. To use the coordinates in the CPU after matching, you must transfer them first.

You could do something like this:

    FeaturesHost* features = new FeaturesHost( lFeatures->getFeatureCount(), lFeatures->getDescriptorCount() );
    features->pin( );
    cudaMemcpy( features->getFeatures(),
                             lFeatures->getFeatures();
                             lFeatures->getFeatureCount() * sizeof(Feature),
                             cudaMemcpyDeviceToHost );
    cudaMemcpy( features->getDescriptors(),
                             lFeatures->getDescriptors(),
                             lFeatures->getDescriptorCount() * sizeof(Descriptor),
                             cudaMemcpyDeviceToHost );
    features->unpin( );

I tried and it worked! Thank you so much!

[gloria111]

it works,thanks

[gloria111]

I try to get all the descriptors and feature points on the CPU with following codes
std::unique_ptr<popsift::Features> sf;
sf.reset(sfeatures);
popsift::Feature* sfeature_list = sf->getFeatures();
std::vector<float> spoints(4 * numFeatures);
std::vector<float> sdesc(128 * numFeatures);
int width = 1920;
int height = 1080;

for(size_t i = 0; i < numFeatures; i++) { popsift::Feature pFeat = sfeature_list[i];
but the program crashes when i try to print the descriptors.

    cout << "pFeat.desc->features:" << ((pFeat.desc[0])->features[0[)<< endl;
    for(int oriIdx = 0; oriIdx < pFeat.num_ori; oriIdx++)
    {
        const popsift::Descriptor* pDesc = pFeat.desc[oriIdx];
        cout << "note here :" << ((pDesc->features)[0]) << endl;
        for(int k = 0; k < 128; k++)
        {
            sdesc[128 * i + k] = pDesc->features[k]; //==(*pDesc).features[k]
        }

        spoints[4 * i + 0] = std::min<float>(std::round(pFeat.xpos), width - 1);
        spoints[4 * i + 1] = std::min<float>(std::round(pFeat.ypos), height - 1);
        spoints[4 * i + 2] = pFeat.sigma;
        spoints[4 * i + 3] = pFeat.orientation[oriIdx];
    }
}