{"action":"created","issue":{"url":"https://api.github.com/repos/ARM-DOE/pyart/issues/294","labels_url":"https://api.github.com/repos/ARM-DOE/pyart/issues/294/labels{/name}","comments_url":"https://api.github.com/repos/ARM-DOE/pyart/issues/294/comments","events_url":"https://api.github.com/repos/ARM-DOE/pyart/issues/294/events","html_url":"https://github.com/ARM-DOE/pyart/issues/294","id":76868656,"number":294,"title":"Projection issue for VERY large mosiac","user":{"login":"scollis","id":825351,"avatar_url":"https://avatars.githubusercontent.com/u/825351?v=3","gravatar_id":"","url":"https://api.github.com/users/scollis","html_url":"https://github.com/scollis","followers_url":"https://api.github.com/users/scollis/followers","following_url":"https://api.github.com/users/scollis/following{/other_user}","gists_url":"https://api.github.com/users/scollis/gists{/gist_id}","starred_url":"https://api.github.com/users/scollis/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/scollis/subscriptions","organizations_url":"https://api.github.com/users/scollis/orgs","repos_url":"https://api.github.com/users/scollis/repos","events_url":"https://api.github.com/users/scollis/events{/privacy}","received_events_url":"https://api.github.com/users/scollis/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/ARM-DOE/pyart/labels/component:%20pyart.map","name":"component: pyart.map","color":"207de5"},{"url":"https://api.github.com/repos/ARM-DOE/pyart/labels/Defect","name":"Defect","color":"fc2929"}],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":10,"created_at":"2015-05-15T21:49:21Z","updated_at":"2015-06-19T02:34:25Z","closed_at":null,"body":"So this is one for the GIS crowd. Using Jonathan's new gridding engine I am doing a massive CONUS wide mesh.. But as you can see form the plot, unless we have radars off the eastern seaboard the mesh does not line up with the map.. \r\n\r\nCode: https://github.com/scollis/conus_mosiac/blob/master/scripts/conus_mosiac.py#L76\r\n\r\n![diag_20150513_200000](https://cloud.githubusercontent.com/assets/825351/7662451/2d078736-fb22-11e4-9bc9-470711805e0e.png)\r\n"},"comment":{"url":"https://api.github.com/repos/ARM-DOE/pyart/issues/comments/113346582","html_url":"https://github.com/ARM-DOE/pyart/issues/294#issuecomment-113346582","issue_url":"https://api.github.com/repos/ARM-DOE/pyart/issues/294","id":113346582,"user":{"login":"gamaanderson","id":7915525,"avatar_url":"https://avatars.githubusercontent.com/u/7915525?v=3","gravatar_id":"","url":"https://api.github.com/users/gamaanderson","html_url":"https://github.com/gamaanderson","followers_url":"https://api.github.com/users/gamaanderson/followers","following_url":"https://api.github.com/users/gamaanderson/following{/other_user}","gists_url":"https://api.github.com/users/gamaanderson/gists{/gist_id}","starred_url":"https://api.github.com/users/gamaanderson/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/gamaanderson/subscriptions","organizations_url":"https://api.github.com/users/gamaanderson/orgs","repos_url":"https://api.github.com/users/gamaanderson/repos","events_url":"https://api.github.com/users/gamaanderson/events{/privacy}","received_events_url":"https://api.github.com/users/gamaanderson/received_events","type":"User","site_admin":false},"created_at":"2015-06-19T02:34:25Z","updated_at":"2015-06-19T02:34:25Z","body":"I just realized this today, there is one more issue that you may want to take a look while fixing this.\r\nSome projection assumption are inconsistent, I will resume everything:\r\n\r\n* line [466](https://github.com/ARM-DOE/pyart/blob/master/pyart/map/grid_mapper.py#L466) uses function [corner_to_point](https://github.com/ARM-DOE/pyart/blob/master/pyart/graph/common.py#L28) that uses a local approximation of the [Sinusoidal projection](https://en.wikipedia.org/wiki/Sinusoidal_projection), although I don't think this was a conscious decision\r\n\r\n* line [473](https://github.com/ARM-DOE/pyart/blob/master/pyart/map/grid_mapper.py#L473) uses function [radar_coords_to_cart](https://github.com/ARM-DOE/pyart/blob/master/pyart/io/common.py#L61) which assumes [Azimuthal equidistant projection](https://en.wikipedia.org/?title=Azimuthal_equidistant_projection)\r\n\r\n* lines [479 and 480](https://github.com/ARM-DOE/pyart/blob/master/pyart/map/grid_mapper.py#L479-L480) by summing are doing a euclidean translation and therefore using a flat Earth model (FYI this is not choosing a projection, but actually a [connection](https://en.wikipedia.org/wiki/Connection_%28mathematics%29) #fancyMathematics)\r\n\r\n* I'm not sure how plotting is being done, must give a look into that also\r\n\r\nPoint 2 is probably your goal so this is correct, point 1 is the bug that created this issue and point 3 is limited to the radar range so its errors are smaller.\r\nPoint 1 can be solved implementing Azimuthal equidistant transformation, its a big formula, but I have it somewhere. Points 3 would be probably better use pyProj, but anyway it will have some significant lost of time for little or non improvement in the results."}}