# Using solvePnP with fixed center of rotation

We're using solvePnP to determine the attitude of an object with its center of rotation fixed relative to the camera (object has some aruco markers on it). And I know for a fact that coordinates of the center of the object are constant. Those coordinates are in `tvec`

returned from solvePnP. I just need the object's rotation `rvec`

, but solvePnP doesn't seem to provide a way to tell it that there's no need to optimize `tvec`

because I already know it. The optimization process would have been easier, faster and most importantly *more accurate* if we had a way to do that, but judging by the code of `cvFindExtrinsicCameraParams2`

function it's not the case. At least not for `SOLVEPNP_ITERATIVE`

algorithm that we're using.

So is there a way to use solvePnP to only optimize rotation if I already know `tvec`

? I know that I can provide it as initial guess, but I want to exclude it from optimization altogether.

Thanks!