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2019-10-15 18:26:16 -0500 commented answer Clarification of PnP variants

If you wanted to, you could go into solvepnp.cpp and uncomment the branches for UPNP and DLS. I have tried the DLS branc

2019-10-10 16:59:34 -0500 answered a question solvePnP object pose for Omnidirectional model

You could use omnidir from the contribs or fisheye. omnidir has a much better distortion model than fisheye, but it's a

2019-06-27 13:50:00 -0500 answered a question Find Peaks in Histogram

The general term for a histogram peak in statistics is "mode," (see for example https://link.springer.com/chapter/10.100

2016-02-01 00:24:46 -0500 commented question Sobel derivatives in the 45 and 135 degree direction

Kind of like this

getDerivKernels(kx,ky, 0,1, 7);
k=kx*ky.t();                      
warpAffine(k,kr,getRotationMatrix2D(Point2f(3,3),angle,1.),Size(7,7));
filter2D(ftemp,grad,CV_32F,kr);
2016-02-01 00:24:45 -0500 commented question Sobel derivatives in the 45 and 135 degree direction

For the 45 and 135, you want one of the "Kirsch" or "compass" operators. It's basically`

-2 -1 0
-1  0 1
 0  1 2

and the various symmetries. In general, what you can do is rotate the Sobel kernel with warpAffine instead of the image. Like turn the lightbulb instead of the ladder. For anything but the orthogonals and diagonals, I'd recommend using a larger kernel than 3x3 though to get good results.