print composer & wms layers (max size)

[lutra]

When printing a layout that contains a WMS layer QGIS warns the user that some servers (such UMN Mapserver) only serve images of a certain size, so if the map size in the layout is bigger than the size allowed the resulting pdf/print will show a white rectangle.

The workarounds are two:

*) lower the number of DPIs, but this will produce obviously prints with a lower quality

*) (if you have control over the server configuration) allow the server to serve bigger images: this is not really a optimal solution because usually people does not own the wms server they need to use and also because allowing the server to serve bigger image can be a problem in public wms services.

Other GIS (both proprietary and OS) packages seems to not suffer of this limitation as one can print large formats with WMS layers in it, even if the server is configured to serve small images.

Looking into the PDFs produced by this packages it results that the printed map from the WMS server is tiled, making clear what kind of workaround is used.

It will be nice in the future to have this feature in QGIS.

[jef]

the attached patch adds the opportunity to set tile sizes (eg. 256x256) and then splits up the WMS request into multiple requests.

[jef]

limit and split wms getmap requests to a given tile size.

[lutra]

Hi Jurgen, many, many thanks for looking into this and for the patch. I'm still testing it and I'll give feedback asap.

Meanwhile it seems to me that this patch fixes the problem described here #1576.

[jef]

applied in commit:d508f56a