{"action":"opened","issue":{"url":"https://api.github.com/repos/mapserver/mapcache/issues/134","labels_url":"https://api.github.com/repos/mapserver/mapcache/issues/134/labels{/name}","comments_url":"https://api.github.com/repos/mapserver/mapcache/issues/134/comments","events_url":"https://api.github.com/repos/mapserver/mapcache/issues/134/events","html_url":"https://github.com/mapserver/mapcache/issues/134","id":114735551,"number":134,"title":"Partially-rendered WMS request via MapCache with metatiling","user":{"login":"maddenp","id":1868662,"avatar_url":"https://avatars.githubusercontent.com/u/1868662?v=3","gravatar_id":"","url":"https://api.github.com/users/maddenp","html_url":"https://github.com/maddenp","followers_url":"https://api.github.com/users/maddenp/followers","following_url":"https://api.github.com/users/maddenp/following{/other_user}","gists_url":"https://api.github.com/users/maddenp/gists{/gist_id}","starred_url":"https://api.github.com/users/maddenp/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/maddenp/subscriptions","organizations_url":"https://api.github.com/users/maddenp/orgs","repos_url":"https://api.github.com/users/maddenp/repos","events_url":"https://api.github.com/users/maddenp/events{/privacy}","received_events_url":"https://api.github.com/users/maddenp/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":0,"created_at":"2015-11-03T03:28:30Z","updated_at":"2015-11-03T03:28:30Z","closed_at":null,"body":"I have been having a problem with WMS requests at certain zoom levels returning only partial maps when metatiling is enabled. To demonstrate, consider these requests, made directly on my MapServer / MapCache system:\r\n```\r\n% wget \"http://localhost:8080/mapserv/?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&TRANSPARENT=true&LAYERS=GLIMS_GLACIERS&CRS=EPSG%3A3857&STYLES=&WIDTH=2880&HEIGHT=907&BBOX=-18339451.266430914%2C5959407.98948631%2C-4250578.212907228%2C10396424.60738422\" -O mapserver_direct.png\r\n\r\n% wget \"http://localhost/?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&TRANSPARENT=true&LAYERS=GLIMS_GLACIERS&CRS=EPSG%3A3857&STYLES=&WIDTH=2880&HEIGHT=907&BBOX=-18339451.266430914%2C5959407.98948631%2C-4250578.212907228%2C10396424.60738422\" -O mapcache_metatiling_on.png\r\n\r\n% wget \"http://localhost/?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&TRANSPARENT=true&LAYERS=GLIMS_GLACIERS&CRS=EPSG%3A3857&STYLES=&WIDTH=2880&HEIGHT=907&BBOX=-18339451.266430914%2C5959407.98948631%2C-4250578.212907228%2C10396424.60738422\" -O mapcache_metatiling_off.png\r\n```\r\nI am running MapServer on port 8080, and only on localhost, so the first request goes directly to MapServer.\r\n\r\nFor the second request, I deleted the sqlite3 cache file and restarted Apache. My mapcache.xml contains, in its single &lt;tileset&gt; block:\r\n```\r\n<metatile>2 2</metatile>\r\n<metabuffer>10</metabuffer>\r\n```\r\nFor the third request, I removed the &lt;metatile&gt; and &lt;metabuffer&gt; entries, deleted the sqlite3 cache file and restarted Apache.\r\n\r\nThe resultant image files are attached. The image returned by MapCache without metatiling is essentially identical to the one returned directly by MapServer (the image shows glaciers in Alaska on the left, in and in Greenland on the right). In the image returned by MapCache with metatiling, the glaciers in western North America are missing. The problem appears in just two zoom levels; at all other levels, the Alaskan glaciers appear. And, by only changing the &lt;metatile&gt; tag, I can push the problem to different zoom levels -- but cannot seem to get rid of it.\r\n\r\nMaybe this is a configuration problem and not a bug. I would be grateful for any ideas, and happy to answer any questions.\r\n\r\nThis is MapServer 7.0 and MapCache commit f10eb9bd5a35009a0fe23b52a27ae8cf19ec1932, both built from source on Ubuntu 14.04.\r\n![mapcache_metatiling_off](https://cloud.githubusercontent.com/assets/1868662/10900702/3b00b452-81a0-11e5-9f7a-677dbd619bf1.png)\r\n![mapcache_metatiling_on](https://cloud.githubusercontent.com/assets/1868662/10900704/3b031e2c-81a0-11e5-9e76-ef86aff5c160.png)\r\n![mapserver_direct](https://cloud.githubusercontent.com/assets/1868662/10900703/3b0256f4-81a0-11e5-8317-b1957c5ebf91.png)\r\n\r\n\r\n"}}