"Wrong usage of OpenCV's Eigen utility header. Include Eigen's headers first.

"
This error message occurs when the user tries to include OpenCV's Eigen utility header without including Eigen's headers first. Eigen is a third-party linear algebra library that OpenCV uses for some of its operations.

To fix this error, the user should include Eigen's headers before including any OpenCV headers that use Eigen. This can be done by adding the following line at the beginning of the file:

#include <Eigen/Core>

After including Eigen's headers, the user can then include any OpenCV headers that use Eigen without encountering this error.