opencvmat

Why are the results different when multiplying OpenCV Mats?

Here is a 4x4 transformMatrix Mat.

1.000, 0.000, -0.004, 0.784,
-0.000, 1.000, 0.001, -0.205,
0.004, -0.001, 1.000, -1.435,
0.000, 0.000, 0.000, 1.000

Here is a 3-dimension vector

507.347,359.172,229.584

I performed the OpenCV Mat multiplication operation as follows

double data[] = { 507.347, 359.172, 229.584, 1 };

cv::Mat s(4, 1, CV_64F, data);
cv::Mat d = transformMatrix * s;

The output result is as follows, but it differs from the value calculated using a calculator.

OpenCV Mat Multiply result = matrix * (507.347,359.172,229.584) = (507.394,359.158,229.605)

Calculation result = 507.213, 359.197, 230.538

Why is the result different? Is there something wrong with the code?

Solution

  • I tried this code (C++):

    cv::Matx<double,4,4> M =
{
    1.000, 0.000, -0.004, 0.784,
    -0.000, 1.000, 0.001, -0.205,
    0.004, -0.001, 1.000, -1.435,
    0.000, 0.000, 0.000, 1.000
};

double data[] = { 507.347, 359.172, 229.584, 1 };
cv::Mat s(4, 1, CV_64F, data);

auto Result = M * s;
std::cout << Result;

    But, output becomes:

    [507.212664;
 359.196584;
 229.819216;
 1]

    not reproduce your result.

    Perhaps, value of matrix you see is too low accuracy ?