{"action":"created","issue":{"url":"https://api.github.com/repos/AtsushiSakai/PythonRobotics/issues/127","repository_url":"https://api.github.com/repos/AtsushiSakai/PythonRobotics","labels_url":"https://api.github.com/repos/AtsushiSakai/PythonRobotics/issues/127/labels{/name}","comments_url":"https://api.github.com/repos/AtsushiSakai/PythonRobotics/issues/127/comments","events_url":"https://api.github.com/repos/AtsushiSakai/PythonRobotics/issues/127/events","html_url":"https://github.com/AtsushiSakai/PythonRobotics/pull/127","id":378124613,"node_id":"MDExOlB1bGxSZXF1ZXN0MjI4OTA0NTI4","number":127,"title":"fix EKF","user":{"login":"y011d4","id":27393930,"node_id":"MDQ6VXNlcjI3MzkzOTMw","avatar_url":"https://avatars2.githubusercontent.com/u/27393930?v=4","gravatar_id":"","url":"https://api.github.com/users/y011d4","html_url":"https://github.com/y011d4","followers_url":"https://api.github.com/users/y011d4/followers","following_url":"https://api.github.com/users/y011d4/following{/other_user}","gists_url":"https://api.github.com/users/y011d4/gists{/gist_id}","starred_url":"https://api.github.com/users/y011d4/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/y011d4/subscriptions","organizations_url":"https://api.github.com/users/y011d4/orgs","repos_url":"https://api.github.com/users/y011d4/repos","events_url":"https://api.github.com/users/y011d4/events{/privacy}","received_events_url":"https://api.github.com/users/y011d4/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":3,"created_at":"2018-11-07T03:10:16Z","updated_at":"2018-11-07T17:21:26Z","closed_at":null,"author_association":"NONE","pull_request":{"url":"https://api.github.com/repos/AtsushiSakai/PythonRobotics/pulls/127","html_url":"https://github.com/AtsushiSakai/PythonRobotics/pull/127","diff_url":"https://github.com/AtsushiSakai/PythonRobotics/pull/127.diff","patch_url":"https://github.com/AtsushiSakai/PythonRobotics/pull/127.patch"},"body":"* In `efk_estimation`, the prediction step of `PPred` seems to be an typo (matrix multiplication of `np.array` should be described by not `*` but `np.dot`).\r\n* If I understand correctly, the calculation of `xPred` should not contain noise. So not `ud` but `u` should be used.\r\n* In `observation`, noise in control is described as `Rsim` and one in observation is as `Qsim`, while in `efk_estimation`  `Q` and `R`. I think those notations should be unified (I adopted the same notation as the book, *Probabilistic Robotics*).\r\n\r\nThe comments below, about which I fixed nothing at all, contains my questions about the simulation implemented in EKF algorithm. I have no confidence because I'm just a beginner for this field.\r\n\r\n* Aren't roles `xTrue` and `xDR` opposite? The true trajectory is determined by the control including noise.\r\n* Accordingly the position observation should be changed so that it detects the `xDR` plus noise."},"comment":{"url":"https://api.github.com/repos/AtsushiSakai/PythonRobotics/issues/comments/436705302","html_url":"https://github.com/AtsushiSakai/PythonRobotics/pull/127#issuecomment-436705302","issue_url":"https://api.github.com/repos/AtsushiSakai/PythonRobotics/issues/127","id":436705302,"node_id":"MDEyOklzc3VlQ29tbWVudDQzNjcwNTMwMg==","user":{"login":"y011d4","id":27393930,"node_id":"MDQ6VXNlcjI3MzkzOTMw","avatar_url":"https://avatars2.githubusercontent.com/u/27393930?v=4","gravatar_id":"","url":"https://api.github.com/users/y011d4","html_url":"https://github.com/y011d4","followers_url":"https://api.github.com/users/y011d4/followers","following_url":"https://api.github.com/users/y011d4/following{/other_user}","gists_url":"https://api.github.com/users/y011d4/gists{/gist_id}","starred_url":"https://api.github.com/users/y011d4/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/y011d4/subscriptions","organizations_url":"https://api.github.com/users/y011d4/orgs","repos_url":"https://api.github.com/users/y011d4/repos","events_url":"https://api.github.com/users/y011d4/events{/privacy}","received_events_url":"https://api.github.com/users/y011d4/received_events","type":"User","site_admin":false},"created_at":"2018-11-07T17:21:26Z","updated_at":"2018-11-07T17:21:26Z","author_association":"NONE","body":"> However, I don't agree this:\r\n\r\n  >> If I understand correctly, the calculation of xPred should not contain noise. So not ud but u should be used.\r\n\r\n> Because, the EKF estimation can only use ud (input with noise) because all sensor has noise.\r\n> What do you think?\r\n\r\nI thought that `u` is the control value we want to apply and `ud` is the exact control value the GOD only knows, so we cannot obtain `ud`.\r\nBut it seems that the value `ud` can be obtained somehow. I took a mistake about considered situations.\r\nThank you for your kindful comments!\r\n\r\nI fixed some as you pointed out."}}
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