payload: {"action":"opened","issue":{"url":"https://api.github.com/repos/orbingol/NURBS-Python/issues/67","repository_url":"https://api.github.com/repos/orbingol/NURBS-Python","labels_url":"https://api.github.com/repos/orbingol/NURBS-Python/issues/67/labels{/name}","comments_url":"https://api.github.com/repos/orbingol/NURBS-Python/issues/67/comments","events_url":"https://api.github.com/repos/orbingol/NURBS-Python/issues/67/events","html_url":"https://github.com/orbingol/NURBS-Python/issues/67","id":499953358,"node_id":"MDU6SXNzdWU0OTk5NTMzNTg=","number":67,"title":"NURBS derivatives","user":{"login":"cshorler","id":959792,"node_id":"MDQ6VXNlcjk1OTc5Mg==","avatar_url":"https://avatars3.githubusercontent.com/u/959792?v=4","gravatar_id":"","url":"https://api.github.com/users/cshorler","html_url":"https://github.com/cshorler","followers_url":"https://api.github.com/users/cshorler/followers","following_url":"https://api.github.com/users/cshorler/following{/other_user}","gists_url":"https://api.github.com/users/cshorler/gists{/gist_id}","starred_url":"https://api.github.com/users/cshorler/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/cshorler/subscriptions","organizations_url":"https://api.github.com/users/cshorler/orgs","repos_url":"https://api.github.com/users/cshorler/repos","events_url":"https://api.github.com/users/cshorler/events{/privacy}","received_events_url":"https://api.github.com/users/cshorler/received_events","type":"User","site_admin":false},"labels":[{"id":371230288,"node_id":"MDU6TGFiZWwzNzEyMzAyODg=","url":"https://api.github.com/repos/orbingol/NURBS-Python/labels/bug","name":"bug","color":"d73a4a","default":true}],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2019-09-29T18:36:20Z","updated_at":"2019-09-29T18:36:20Z","closed_at":null,"author_association":"CONTRIBUTOR","body":"I made a test of NURBS derivatives using a circle, I don't believe the outputs to be correct (see picture).  I also note that NURBS derivatives are documented in more recent papers than the NURBS book - so perhaps this isn't expected to work.\r\n\r\nI'll provide a test for this at the next opportunity\r\n\r\nManually (Tested on Linux & Windows, Python 2 & 3):\r\n\r\n1. Create a 7pt NURBS circle (also not convinced the 7pt construction in geomdl.shapes is correct after my back of the envelope calculation for a unit circle - it looks isosceles rather than equilateral?).  Also tested with 9pt (see picture)\r\n\r\n2. Create derivatives\r\n\r\n3. Plot the results\r\n\r\nI was expecting circles.\r\n![circles_and_first_derivatives](https://user-images.githubusercontent.com/959792/65837463-a7b18180-e2ef-11e9-8b82-e8ee209224f8.png)\r\n\r\n\r\n"}}
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