Sentinel Stereo Camera calibration inconsistency

  • Hello,

    When running voxl-calibrate-camera on a VOXL2 Sentinel drone, we have struggled to consistently recalibrate the cameras and usually are stuck for long periods of time trying to calibrate one or two "red box" steps of the process. We've achieved successful calibration attempts before, but we cannot do this consistently. Do you have a recommended calibration board size/setting, or a recommended backing for the calibration board? We currently have tried using an opencv 9x6 chessboard with square length of 0.02143 and 0.073 meters

    The commands we are running, for each respective board size, are:
    voxl-calibrate-camera stereo_front -l 9x6 -s 0.02143
    voxl-calibrate-camera stereo_front -l 9x6 -s 0.073

  • Dev Team

    We use a 5x6 board with 65.5mm squares consistently in production

  • @Chad-Sweet Even with a similar board size (5x6, 55 mm), we have been struggling to account for reprojection error on both VOXL1 and VOXL2. Strangely enough, VOXL1 has been more consistent in terms of less reprojection error. Before running voxl-calibrate-camera, we used voxl-configure-extrinsics to ensure the correct extrinsic was matched to the proper drone. Is there something about how we are tuning the stereo cameras on both the VOXL1 and VOXL2 such that we create additional reprojection error? The videos of us calibrating the cameras on both VOXL boards are in the link below:

  • Dev Team

    @Daniel-Ryu The stereo sensors' lens can be adjusted which will change their focus. Looking at the videos you provided it seems to me that you should be able to achieve a lower reprojection error if you adjust the focus on the units. It looks like the VOXL1 is getting a better reprojection error number because the cameras are fairly close to in focus and there isn't much blurr/fuzz in the video stream. On your VOXL2 setup it looks to me that either the camera is out of focus or the lens is dirty.

    To adjust the focus on our stereo cameras twist the lens housing clockwise or counterclockwise similarly to how you would on a DSLR lens. Look closely at the stereo cams and you will see 4 flat edges. I recommend using a 6mm wrench to engage 2 of the flat edges; from there you'll be able to rotate and adjust the lens as needed. It is possible to use something like tweezers or small pliers to accomplish this however I recommend against that method because it is too easy for the tool to slip off and end up scratching the lens.

    To clean the lens I recommend using a clean microfiber cloth, a lens tissue, or a fresh q-tip

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