[QGIS-Developer] QGIS WCS is requesting FULL dataset?

Jonathan Moules jonathan-lists at lightpear.com
Sat Oct 13 07:50:22 PDT 2018

Hi Richard,

I don't know about the QGIS side, but from the server side I'd agree 
with your assessment.

The WCS 1.0 spec says that the server will use the interpolation method 
specified in the getcapabilities (or if none is defined (as here), then 
assume Nearest Neighbour) for alternative widths/heights.

Having to interpolate an entire country down to a 10x10 grid seems 
utterly bonkers for a WCS. Even WMS (where you will have overviews so 
it'll be massively faster) I can't think of why you'd want a tiny 10x10 

Maybe this is QGIS's way of trying to creating a WCS legend icon?

Whatever the reason, I'd suggest raising it as a bug report as it's not 
going to be doing any favours to the WCS servers for no real benefit.



On 2018-10-12 11:48, Richard Duivenvoorde wrote:
> Hi,
> using our national DEM WCS:
> https://geodata.nationaalgeoregister.nl/ahn3/wcs?
> Loading the layer ahn3_5m_dtm for an area of a couple of km in
> epsg:28992 is very slow.
> I'm not so familiar with the WCS specs, but I see QGIS asking:
> https://geodata.nationaalgeoregister.nl/ahn3/wcs?SERVICE=WCS&VERSION=1.0.0&REQUEST=GetCoverage&FORMAT=GEOTIFF_FLOAT32&COVERAGE=ahn3_5m_dtm&BBOX=10000,250000,356250,618750&CRS=EPSG:28992&RESPONSE_CRS=EPSG:28992&WIDTH=10&HEIGHT=10
> which is the whole of the Netherlands (in a 10x10 pixel output??) and
> after that a more proper bbox.
> Is this supposed to go like this?
> I reckon that (if the WCS data does not have overviews), loading the
> whole dataset all the time is pretty intensive.
> Anybody more familiar with this can tell something about this?
> Regards,
> Richard Duivenvoorde
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