[OSM-talk] Osmarender, bridges, layers and seams

[80n]

It is a bug.  The seams are a rendering artifact and should definitely not
be worked-around by adjusting the tagging.

On Tue, Mar 11, 2008 at 10:21 PM, Dermot McNally <dermotm at gmail.com> wrote:

> The matter of renderer quirks and whether you should work around them
> arose on another thread but didn't really go places. One principle
> that was strongly backed was "fix the renderer, don't tamper with the
> data". But before filing any bug reports I want to check the mood
> among those of you hacking on the renderers, particularly
> osmarender...
>
> As of one of the major version bumps in osmarender, the way that
> "normal" (definition below) bridges were rendered changed. Consider
> the following ascii art to be a rendered bridge:
>
>  0
>  0
>  0
>  0
>  0
> |1|
> |1|
> |1|
> |1|
> |1|
>  0
>  0
>  0
>  0
>  0
>
> IOW, we have the bridge portion itself, which is a way having layer=1
> and bridge=yes. Abutting it are ways not having either of these,
> therefore implicitly at layer=0. Previously, this would be rendered as
> a continuous road of whatever type with "bridge-marks" alongside the
> part so-tagged. Brilliant. However, for a while now, an unsightly seam
> has been getting shown at the transition.
>
> This has led at least one mapper to get creative (IMHO unreasonably
> so) with the layer attribute. For example, to work around the seams in
> the above case, you might do the following:
>
>  0
>  0
>  1
>  1
>  1
> |1|
> |1|
> |1|
> |1|
> |1|
>  1
>  1
>  1
>  0
>  0
>
> This troubles me, though. Firstly, it's less "correct" in the layering
> it implies. Secondly, you still get your seam, it just moves away from
> the bridge boundary.
>
> So is there any reason we can't get rid of these seams? Their presence
> is a temptation to adopt workarounds. Those workarounds have already
> cost me a lot of effort reinstating good data destroyed as a result of
> rework that would never have been performed if the seams hadn't been
> showing.
>
> Do they serve any purpose? Is it hard to avoid them?
>
> Thanks,
> Dermot
>
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