[Qgis-developer] Tiled web maps in QGIS

[Alex Mandel]

On 03/11/2013 06:45 AM, Jochen Topf wrote:
> Hi!
>
> I missed support for easily using web tile servers in QGIS for a long time and
> finally decided to do something about it. :-) (I am not talking about WMS-type
> servers, only about those where all you have is a URL pattern such as
> http://tile.openstreetmap.org/${z}/${x}/${y}.png .)
>
> Somebody wrote down how this can be done with QGIS using GDAL:
> http://www.3liz.com/blog/rldhont/index.php?post/2012/07/17/OpenStreetMap-Tiles-in-QGIS
> Thats already pretty impressive, but it is harder than it should be. So I
> started working on a plugin: https://github.com/joto/qgis-plugin-tiled-map .
> This will give you a menu where you can easily add servers that are pre-defined
> in a .yaml file. (Of course this should be configurable from QGIS at some
> point.)
>
> Now to my question: This works all very well and does mostly what I want.
> But there is one issue: Of course QGIS/GDAL will resize the tiles from the
> servers to fit the current screen. That's okay in many cases. But I want
> to at least have the option of "snapping" to the right resolutions (will,
> of course, only work in EPSG:3857).
>
> There is already "Tile scale" panel that is used for WMS-C. Can I somehow
> enable this from my plugin? I looked into the core C++ code and it looks
> like it is very specifically tied to one data provider:
>
>    if ( !rl || rl->providerType() != "wms" || !rl->dataProvider() )
>      return;
>
> Maybe this can be done in a more general way?
>
> Is the "Tile scale" panel the right way to go? I want the user to have the
> choice whether they want the snapping or not. I am not sure how the panel
> is supposed to work in that case.
>
> Jochen
>

FYI, the openlayers plugin is essentially doing something very similar.
Your scale issue might be similar to what Nathan was seeing yesterday 
too where tiles don't always line up right.

Thanks,
Alex