On Thu, Oct 15, 2015, at 05:28 AM, Jussila Ville wrote: > Hi Kevin
> Thanks for your reply. That helped me a lot. I’m using Geoserver with the direct integration of GWC, so I’m more interested about that at the moment. Yes, that's what I was describing. > What do you mean ”if the request does align (to the grid)…”? The > request coordinate system is set to be the same as the cached layer’s > coordinates system? > The tiles form a specific grid within that coordinate system. The cache only works when the request bounding box and pixel dimensions match the bounds and size of a specific cell in the grid. If the grid starts at 0,0, and chops 100x100 unit squares in map coordinate that are 256x256 px then a box from 300,400 to 400,500 that's 256x256 px aligns with the grid. One from 350,450 to 450,550 that's 256x256px does not, neither does one that's 512x512px, neither does one that's 100 map units tall but 200 wide. > > How does the Geoserver choose which set of the preseeded tiles it is > using at different zoom levels? Is there any tolerance or does it has > to be the exact scale from the gridset when it returns the tile, otherwise it cache it? GeoServer doesn't know anything about the tiles in its embeded GeoWebCache. It just asks GWC if it can handle the request and if so, lets it. GWC has some wiggle room for WMS-C requests. WMTS and TMS use exact integer indices in the grid rather than bounding boxes in map coordinates which eliminates the need for this. It's not just a matter of scale but also of the dimensions and alignment of the request. You may be after a feature called FullWMS which allows GWC (whether embedded within GeoServer or not) to respond to arbitrary requests as long as the CRS matches rather than requiring exact matches to the tiles. FullWMS is described here: http://docs.geoserver.org/latest/en/user/geowebcache/using.html#geowebcache-endpoint-url -- Kevin Michael Smith [email protected]
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