C++ OpenCV词汇包：断言失败（！\u descriptors.empty（））

我正在尝试创建一包单词，以便以后可以训练SVM。我是OpenCV新手，所以我使用了在互联网上找到的代码。问题是我有以下错误：

OpenCV Error: Assertion failed (!_descriptors.empty()) in add, file /build/buildd/opencv-2.4.8+dfsg1/modules/features2d/src/bagofwords.cpp, line 57
terminate called after throwing an instance of 'cv::Exception'
  what():  /build/buildd/opencv-2.4.8+dfsg1/modules/features2d/src/bagofwords.cpp:57: error: (-215) !_descriptors.empty() in function add

Aborted (core dumped)

代码如下：

#include <stdio.h>
#include <stdlib.h>

#include <opencv2/opencv.hpp>
#include <fstream>
#include <iostream>
#include <string>

#include <dirent.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>


using namespace cv;
using namespace std;

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

    Ptr<FeatureDetector> features = FeatureDetector::create("FAST");
    Ptr<DescriptorExtractor> descriptors = DescriptorExtractor::create("FAST");
    Ptr<DescriptorMatcher> matcher = DescriptorMatcher::create("FlannBased");

    //defining terms for bowkmeans trainer
    TermCriteria tc(TermCriteria::MAX_ITER + TermCriteria::EPS, 10, 0.001);
    int dictionarySize = 1000;
    int retries = 1;
    int flags = KMEANS_PP_CENTERS;

    BOWKMeansTrainer bow_trainer(dictionarySize, tc, retries, flags);
    BOWImgDescriptorExtractor bowDE(descriptors, matcher);

    //training data now
    Mat mat_features1, mat_features2;

    Mat img = imread("../positive_images/2014-12-07 19-55-07 804ea51d (1).JPG", 0);
    Mat img2 = imread("../positive_images/Pictures23.bmp_0000_0342_0104_0564_0543.png", 0);

    vector<KeyPoint> keypoints, keypoints2;

    features->detect(img, keypoints);
    features->detect(img2,keypoints2);

    descriptors->compute(img, keypoints, mat_features1);
    descriptors->compute(img2, keypoints2, mat_features2);

    bow_trainer.add(mat_features1);
    bow_trainer.add(mat_features2);

    Mat dictionary = bow_trainer.cluster();
    bowDE.setVocabulary(dictionary);

    return 0;
}

你知道可能是什么问题吗？你能告诉我怎么修吗？

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如果您需要我提供更多信息，请告诉我

在文件路径中使用\\而不是/同样，请将文件命名为pictures.png或其他一些简单的名称。我在UBUNTUALS下工作，因此我认为问题不在于名称。FAST只是一个检测器，您不能将其用作描述符。

g++ BOW_creator.cpp -o BOW_creator `pkg-config --cflags --libs opencv`