{"action":"created","issue":{"url":"https://api.github.com/repos/proj4-bot/proj.4/issues/82","labels_url":"https://api.github.com/repos/proj4-bot/proj.4/issues/82/labels{/name}","comments_url":"https://api.github.com/repos/proj4-bot/proj.4/issues/82/comments","events_url":"https://api.github.com/repos/proj4-bot/proj.4/issues/82/events","html_url":"https://github.com/proj4-bot/proj.4/issues/82","id":79090680,"number":82,"title":"tmerc \"back folding\" problems.","user":{"login":"proj4-bot","id":12542084,"avatar_url":"https://avatars.githubusercontent.com/u/12542084?v=3","gravatar_id":"","url":"https://api.github.com/users/proj4-bot","html_url":"https://github.com/proj4-bot","followers_url":"https://api.github.com/users/proj4-bot/followers","following_url":"https://api.github.com/users/proj4-bot/following{/other_user}","gists_url":"https://api.github.com/users/proj4-bot/gists{/gist_id}","starred_url":"https://api.github.com/users/proj4-bot/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/proj4-bot/subscriptions","organizations_url":"https://api.github.com/users/proj4-bot/orgs","repos_url":"https://api.github.com/users/proj4-bot/repos","events_url":"https://api.github.com/users/proj4-bot/events{/privacy}","received_events_url":"https://api.github.com/users/proj4-bot/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/proj4-bot/proj.4/labels/bug","name":"bug","color":"fc2929"},{"url":"https://api.github.com/repos/proj4-bot/proj.4/labels/C:%20Core","name":"C: Core","color":"0000aa"},{"url":"https://api.github.com/repos/proj4-bot/proj.4/labels/P:%20major","name":"P: major","color":"f6f6f6"}],"state":"open","locked":false,"assignee":null,"milestone":{"url":"https://api.github.com/repos/proj4-bot/proj.4/milestones/2","html_url":"https://github.com/proj4-bot/proj.4/milestones/4.7.0","labels_url":"https://api.github.com/repos/proj4-bot/proj.4/milestones/2/labels","id":1123481,"number":2,"title":"4.7.0","description":"None","creator":{"login":"proj4-bot","id":12542084,"avatar_url":"https://avatars.githubusercontent.com/u/12542084?v=3","gravatar_id":"","url":"https://api.github.com/users/proj4-bot","html_url":"https://github.com/proj4-bot","followers_url":"https://api.github.com/users/proj4-bot/followers","following_url":"https://api.github.com/users/proj4-bot/following{/other_user}","gists_url":"https://api.github.com/users/proj4-bot/gists{/gist_id}","starred_url":"https://api.github.com/users/proj4-bot/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/proj4-bot/subscriptions","organizations_url":"https://api.github.com/users/proj4-bot/orgs","repos_url":"https://api.github.com/users/proj4-bot/repos","events_url":"https://api.github.com/users/proj4-bot/events{/privacy}","received_events_url":"https://api.github.com/users/proj4-bot/received_events","type":"User","site_admin":false},"open_issues":4,"closed_issues":11,"state":"closed","created_at":"2015-05-21T15:25:05Z","updated_at":"2015-05-21T17:29:10Z","due_on":"1970-01-01T00:00:00Z","closed_at":"2015-05-21T15:25:05Z"},"comments":4,"created_at":"2015-05-21T17:29:09Z","updated_at":"2015-05-21T17:29:18Z","closed_at":null,"body":"**Reported by warmerdam on 17 Jun 2008 15:46 UTC**\nYou can demonstrate the problem with the PROJ.4 commandline program cs2cs:\r\n\r\n```\r\ncs2cs +proj=latlong +datum=WGS84 +to +proj=utm +zone=32 +datum=WGS84\r\n```\r\n\r\nGive as input, this point in Alaska:\r\n```\r\n-149.66 64.237\r\n```\r\nAnd you get this:\r\n```\r\n522986.92       5029096.80 0.00\r\n```\r\nwhich is somewhere in Italy (near Milan). \r\n\r\nI realize this result is an effect of using tmerc equations far from where they are valid, but it causes serious problems in MapServer when trying to establish which images intersect a target map request.  In this case we have images from around the world, some in relatively local projections like tmerc. We reproject the map request bounds into the target projection and check for overlap. \r\n\r\nWhat I would like is if we could make the tmerc projection fail (ie return HUGE_VAL) for points so far from the central meridian that they are likely to start folding back on themselves. \n\nMigrated-From: https://trac.osgeo.org/proj/ticket/5"},"comment":{"url":"https://api.github.com/repos/proj4-bot/proj.4/issues/comments/104364269","html_url":"https://github.com/proj4-bot/proj.4/issues/82#issuecomment-104364269","issue_url":"https://api.github.com/repos/proj4-bot/proj.4/issues/82","id":104364269,"user":{"login":"proj4-bot","id":12542084,"avatar_url":"https://avatars.githubusercontent.com/u/12542084?v=3","gravatar_id":"","url":"https://api.github.com/users/proj4-bot","html_url":"https://github.com/proj4-bot","followers_url":"https://api.github.com/users/proj4-bot/followers","following_url":"https://api.github.com/users/proj4-bot/following{/other_user}","gists_url":"https://api.github.com/users/proj4-bot/gists{/gist_id}","starred_url":"https://api.github.com/users/proj4-bot/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/proj4-bot/subscriptions","organizations_url":"https://api.github.com/users/proj4-bot/orgs","repos_url":"https://api.github.com/users/proj4-bot/repos","events_url":"https://api.github.com/users/proj4-bot/events{/privacy}","received_events_url":"https://api.github.com/users/proj4-bot/received_events","type":"User","site_admin":false},"created_at":"2015-05-21T17:29:18Z","updated_at":"2015-05-21T17:29:18Z","body":"**Comment by evenden on 18 Jun 2008 17:44 UTC**\nTwo major problems here:\\n\r\n\r\n1. grossly exceeding the defined logitude limits of UTM (nominally +-3.5 degrees from the central meridian and\\n\r\n\r\n2. grossly exceeding the limits of projection tmerc which starts to fall apart beyond 20 degrees from the central meridian.\r\n\r\nI also feel that a great deal of the problem lies in the methodology of the MapServe system.  I would think that there would be failures of other projections that had to \"stretch\" their limits to meet the MapServer coordinate needs.\r\n\r\nLastly, if one needs more extended TM coordinates use the either etmerc, ftmerc or ktmerc.  Ktmerc will be available in the libproj4 library soon.\r\n\r\nIf one insists on the suggested patch to tmerc above, a more practical limit would be around 20 degrees rather than the 90 degrees suggest."}}