Dear Kinovea team, I have noticed a problem with the lens calibration since I have been working with distorted images (Basler camera). When analyzing GoPro images, where no distortion is present, i never experienced any problems. When using distorted Basler videos, I determined the intrinsic camera parameters and distortion coefficients accordingly and entered them into the lens calibration. Next, I used the perspective grid for image calibration at the beginning of each video recording. However, with this procedure, the calibration seems to change with each digitized point, and the calculated coordinates of the same point change with each additional point that I digitize in the video. After one digitized point, I get coordinates of e.g. x=600, y=800. After two digitized points: x=598, y=798. After 15 digitized points: x=570, y=770. So if the calibration is done at the beginning, it will be wrong at the end. (Distorted videos must consequently always be calibrated at the end). (Perhaps camera calibration is applied again with each digitized point and thus leads to an over-correction of the distortion?). Many thanks for your support! Daniel
- joan
- Admin
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Hi,
What version of Kinovea are you using? There were some important changes in 2024.1, it's possible there is a regression I haven't noticed in my testing.
Is the camera static? Are you using camera motion estimation? When you say a digitized point do you mean a new static marker or a new point along a trajectory?
Indeed a given point on a given frame shouldn't change coordinates unless the coordinate system is tracked or the calibration object is tracked, is it your case?
Hi Joan,
Thank you very much for your quick reply! I am unfamiliar with 2024.1. I'm using 2023.1.2. (the same problem exists in 0.9.5). Yes, the camera is static (on a tripod). I am not using camera motion estimation (which is still unknown to me). Yes, I mean a new static marker. I still determine hit performances on a table tennis table manually. Yes, the points on a given frame shouldn't change coordinates. The calibration object is not tracked (I calibrate the image based on the dimensions of the table tennis table). Daniel