opencv: call to "Mat" is ambiguous - c++

Question

I try to use opencv to calculate the HoG descriptor, but an error call to "Mat" is ambiguous was raised.
I saw the answer under Error: Mat is ambiguous when using OpenCV
and I don't know whether my includes are right.
and my includes for opencv are:
#include <opencv2/core/core.hpp>
#include<opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv/cv.hpp>
#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <opencv2/ml/ml.hpp>
#include <string>
using namespace std;
using namespace cv;
using namespace cv::ml;
here's the code:
for (int j = 0; j < original[i]; j++) {
cv::Mat train_original;
train_original = cv::imread(original_path + std::to_string(j) + ".jpg", 1);
cv::resize(train_original, train_resize_image, cv::Size(128, 128), 0, 0, CV_INTER_LINEAR);
// 计算HOG descriptor
cv::HOGDescriptor hog(cv::Size(128, 128), cv::Size(64, 64), cv::Size(16, 16), cv::Size(8, 8), 9);
hog.compute(train_resize_image,train_descriptor);
cv::Mat descriptor_mat(cv::Mat(train_descriptor).t());
train_descriptors.push_back(descriptor_mat);
}
where train_descriptor is in type of std::vector<float>
The error was raised in line
cv::Mat descriptor_mat(cv::Mat(train_descriptor).t());
Any help will be appreciated! thanks!

Answer 1

You should change the following line:
cv::Mat descriptor_mat(cv::Mat(train_descriptor).t());
with
cv::Mat descriptor_mat = cv::Mat(train_descriptor).t();
since Mat operator = can handle MatExpr object, while Mat constructor can not(check OpenCV documentation). But be careful with this method since it does not copy the data and shares it(like a pointer). Basically, if you want to copy the data you can do the following:
cv::Mat descriptor_mat;
cv::transpose(cv::Mat(train_descriptor),descriptor_mat);