Render strokes in real world units

[jerry73204]

Is it possible to render the stroke width in meters, feets? The rendered pixel width depends on zoom and projection. I see an example from GeoServer. It does so by specifying uom.

If mapnik cannot work it out, as an alternative, is it possible to transform a linestring to polygon?

[talaj]

It's not as straightforward as writing stroke-width="10meters", but it is possible.

One way are render-time variables. It is possible to pass a variable to the rendering, let's say a variable @pixels_per_meter and then write a line style such as

<LineSymbolizer stroke-width="10 * @pixels_per_meter">

In postgis, pgraster and newly in sqlite datasources, there are placeholders !pixel_width! and !pixel_height! that you can use in a query

select 10 / !pixel_width! as road_width

and use in style like

<LineSymbolizer stroke-width="[road_width]">

[jerry73204]

Thanks @talaj. The reply is informational.
I found postgis' ST_Buffer and ST_OffsetCurve maybe a good alternative.