Mat数据结构（数组）初始化错误

Question

I am writing a opencv code for particle filter but i am getting some error, i think it is because of the below code.How can i initialise the Mat array at the time of declaration itself?

Mat particle[N];
for (int i = 0; i < N; i++)
    {
        particle[i].at<float>(0, 0) = rec.x + distribution(generator);//x
        particle[i].at<float>(1, 0) = rec.y + distribution(generator);//y
        particle[i].at<float>(2, 0) = 0;//vel(x)
        particle[i].at<float>(3, 0) = 0;//vel(y)
        particle[i].at<float>(4, 0) = min(0.66 + abs(rng.uniform(0, 1)), MAX_a);//a
        particle[i].at<float>(5, 0) = rec.height + 10 + rng.uniform(0, 1);//vel(h)
        weight[i] = 1.0 / N;
    }

Answer 1

Why don't you use std::vector:

std::vector<cv::Mat> particle(N, cv::Mat(6, 1, CV_32F)); // constructor which takes
// number of elems and allocates memory of them using second argument as a prototype object
for (int i = 0; i < N; i++)
    {
        particle[i].at<float>(0, 0) = rec.x + distribution(generator);//x
        particle[i].at<float>(1, 0) = rec.y + distribution(generator);//y
        particle[i].at<float>(2, 0) = 0;//vel(x)
        particle[i].at<float>(3, 0) = 0;//vel(y)
        particle[i].at<float>(4, 0) = min(0.66 + abs(rng.uniform(0, 1)), MAX_a);//a
        particle[i].at<float>(5, 0) = rec.height + 10 + rng.uniform(0, 1);//vel(h)
        weight[i] = 1.0 / N;
    }

We have used following constructor:

explicit vector (size_type n, const value_type& val = value_type(), const allocator_type& alloc = allocator_type());

which Constructs a container with n elements. Each element is a copy of val. ( reference)

And yes, you had a trouble with previous attempt due to built-in array of Mat's objects does not initialize them to proper sizes, what vector's constructor does.