convertPointsFromHomogeneous returning wrong values (Bug #1316)

First of all, converting a single vector using convertFromHomogeneous() can be much slower than doing it by hand. But if you want to do it, use multi-channel mat.

#include "opencv2/calib3d/calib3d.hpp"
#include <stdio.h>

int main(int, char**) {
float v[] = { 1, 2, 3, 4 }, wr3;
cv::Mat V(1, 1, CV_32FC4, v);
cv::Mat W(1, 1, CV_32FC3, w);
cv::convertPointsFromHomogeneous(V, W);
printf("%f %f %f\n", wr0, wr1, wr2);
return 0;
}

That does indeed work. However, the documentation does not say that it only works with multi-channel matrices (why is that??)

http://opencv.itseez.com/modules/calib3d/doc/camera_calibration_and_3d_reconstruction.html?highlight=homogeneous#convertPointsFromHomogeneous

Shouldn't the code I showed initially work as well? Either we should show an example of using the type of vectors I showed, or add to the documentation that the way you showed is the only way.

Also, is there a way to get the equivalent of CV_32FC4 from something that looks more like cv::Mat V(4,1,cv::DataType?<float>::type); ?

Thanks,

David

there is ambiguity. when the function gets 4x1 matrix, it can be either a set of 4 single-element vectors (i.e. scalars) or a single 4-element vector. To avoid this ambiguity, we always treat MxN single-channel matrix as a set of M N-element vectors. Or you can use Mx1 or 1xM N-channel matrix, which is usually a recommended format. You can also use reshape to switch between the formats.