[Qgis-user] WMS Provider and the DPI parameter

[Jürgen E. Fischer]

Hi Andrea,

On Mon, 01. Oct 2012 at 23:16:05 +0200, Andrea Peri wrote:
>    It is a not standard parameter, but main question I have is understand why
>    there is the need to use a "DPI" parameter.

>    Infact the standard wms request contain a bbox and a map pixel dimension.
>    Perhaps I miss something, but AFAIK knowing the BBOX and the Pixel Size
>    Map I guess is possible to calculate the DPI value.

>    So put on a request BBOX, Pixel-SizeMap and DPI seem redundant to me.

Not really.  DPI relates to the output size, not the bounding box.  Unless you
know how large the pixels will be renderer, you don't know the actual DPI.

WMS assumes a fixed pixel size, which usally doesn't match the actual screen
resolution and certainly not a printer's resolution.

Therefore the result of scale calculation on the server side yield different
results from the client.  And I think that's what the DPI parameter is meant to
fix.   BTW geoserver also has a DPI parameter.



Jürgen


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