{"action":"created","issue":{"url":"https://api.github.com/repos/opencv/opencv/issues/7312","repository_url":"https://api.github.com/repos/opencv/opencv","labels_url":"https://api.github.com/repos/opencv/opencv/issues/7312/labels{/name}","comments_url":"https://api.github.com/repos/opencv/opencv/issues/7312/comments","events_url":"https://api.github.com/repos/opencv/opencv/issues/7312/events","html_url":"https://github.com/opencv/opencv/issues/7312","id":177730556,"number":7312,"title":"calibration using circle grid pattern has perspective bias","user":{"login":"leoujz","id":5565643,"avatar_url":"https://avatars.githubusercontent.com/u/5565643?v=3","gravatar_id":"","url":"https://api.github.com/users/leoujz","html_url":"https://github.com/leoujz","followers_url":"https://api.github.com/users/leoujz/followers","following_url":"https://api.github.com/users/leoujz/following{/other_user}","gists_url":"https://api.github.com/users/leoujz/gists{/gist_id}","starred_url":"https://api.github.com/users/leoujz/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/leoujz/subscriptions","organizations_url":"https://api.github.com/users/leoujz/orgs","repos_url":"https://api.github.com/users/leoujz/repos","events_url":"https://api.github.com/users/leoujz/events{/privacy}","received_events_url":"https://api.github.com/users/leoujz/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/opencv/opencv/labels/category:%20calib3d","name":"category: calib3d","color":"ededed"},{"url":"https://api.github.com/repos/opencv/opencv/labels/feature","name":"feature","color":"84b6eb"}],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":2,"created_at":"2016-09-19T08:40:43Z","updated_at":"2016-09-28T19:00:12Z","closed_at":null,"body":"##### Detailed description\r\n\r\nthe perspective bias using circle grid is not considered in the calibrtion pipeline, when using a circle grid pattern, a circle on the board in real world, projects on the image to be an ellipse (unconsidering distortion), according to the projective geometry, the center of the circle does not correspond to the center of the ellipse (or the centroid of the blob), this is showed in the following picture:\r\n\r\nhttp://paste.ubuntu.org.cn/4219097\r\n\r\nthe perspective bias affects the calibration precision, this is detailed in the paper\r\n\r\nHeikkila J. Geometric camera calibration using circular control points[J]. IEEE Transactions on pattern analysis and machine intelligence, 2000, 22(10): 1066-1077.\r\n"},"comment":{"url":"https://api.github.com/repos/opencv/opencv/issues/comments/250265905","html_url":"https://github.com/opencv/opencv/issues/7312#issuecomment-250265905","issue_url":"https://api.github.com/repos/opencv/opencv/issues/7312","id":250265905,"user":{"login":"leoujz","id":5565643,"avatar_url":"https://avatars.githubusercontent.com/u/5565643?v=3","gravatar_id":"","url":"https://api.github.com/users/leoujz","html_url":"https://github.com/leoujz","followers_url":"https://api.github.com/users/leoujz/followers","following_url":"https://api.github.com/users/leoujz/following{/other_user}","gists_url":"https://api.github.com/users/leoujz/gists{/gist_id}","starred_url":"https://api.github.com/users/leoujz/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/leoujz/subscriptions","organizations_url":"https://api.github.com/users/leoujz/orgs","repos_url":"https://api.github.com/users/leoujz/repos","events_url":"https://api.github.com/users/leoujz/events{/privacy}","received_events_url":"https://api.github.com/users/leoujz/received_events","type":"User","site_admin":false},"created_at":"2016-09-28T19:00:12Z","updated_at":"2016-09-28T19:00:12Z","body":"I have tested the Matlab code which is released by the author on the page:\r\nhttp://www.ee.oulu.fi/~jth/calibr/\r\nThe algorithm applies a Q matrix to the input 3D points, but the implementation is quite different with the OpenCV calib3d pipeline.\r\nIt's really difficult for me to apply the bias correction to the OpenCV camera model, especially in the near future. It might be a easier task if familiar with the OpenCV bottom code.\r\nBut I do hope OpenCV calib3d framework would consider the perspective bias, because OpenCV has rich features of camera calibration, and always be the first choice"}}
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