I have many times been looking for a way of expressing literals in sld using
ground units. This could be very useful if one wants to render something,
let's say road lines, approximately 2 meters wide.
So how to accomplish?
I'm thinking that if the query parameters, or at least the current scale
denominator of the request were available as 'variables' or xml entities you
could build up an expression using regular function calls in sld, example:

<CssParameter name="stroke-width">
<ogc:Div>
<!-- My preferred road width expressed in ground units -->
<ogc:Literal>2.0</ogc:Literal>
<!-- The magic value that maps ground units to pixel units -->
<ogc:Literal>&takeMeToPixelUnits;</ogc:Literal>
</ogc:Div>
</CssParameter>

Of course the users display resolution would have to be assumed or else
maybe provided as a vendor parameter in the request.

If someone could point me in the right direction I would be glad to help
implementing.

Best regards 

/Peter

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