SolvePnP with useExtrinsicGuess is broken when using IEnumberable overload

[Jcparkyn]

Summary of your issue

When using Cv2.SolvePnP with the overload that takes IEnumerable parameters, the rvec and tvec values passed to the function are overwritten before calling the native OpenCV method. This is normally fine, but when using useExtrinsicGuess, this results in garbage output.

The InputArray overload doesn't have this issue.

The problem is here, where rvec and tvec are created from scratch, instead of using the passed-in values.

Environment

• Windows 10
• OpenCvSharp4.Windows, Version="4.7.0.20230115"
• F# 7

What did you do when you faced the problem?

Replaced code with InputArray overload, which works as expected.

Example code (F#):

// Dummy values because coming up with a real scenario is hard.
let mutable rvec = null
let mutable tvec = null
while true do
    Cv2.SolvePnP(
        [Point3f(0f, 0f, 0f); Point3f(0f, 0f, 1f); Point3f(0f, 1f, 0f); Point3f(0f, 1f, 1f)],
        [Point2f(0f, 0f); Point2f(0f, 1f); Point2f(1f, 0f); Point2f(1f, 1f)],
        cameraMatrix = array2D [
            [ 1394.6027293299926; 0.; 995.588675691456];
            [0.; 1394.6027293299926; 599.3212928484164];
            [0.; 0.; 1. ]],
        distCoeffs = [ 0.11; -0.219; 0.0012; 0.00856; 0.1127 ],
        rvec = &rvec,
        tvec = &tvec,
        useExtrinsicGuess = (not <| isNull rvec),
        flags = SolvePnPFlags.Iterative
    )

Output:

rvec and tvec have reasonable values, or at least close to what they are with useExtrinsicGuess=false.

What did you intend to be?

rvec and tvec are not even close to correct.