[talk-au] navit and bays/coastline around Sydney

Franc Carter franc.carter at gmail.com
Tue Apr 26 13:40:23 BST 2011


[snip]

>
> I've been aiming to tag bays as areas rather than just a node in the
> centre. As a consequence my initial thought was to tag the area as
> natural=bay. Traditionally most renderers didn't render this as water.
> the OSM Mapnik style now does, but many others still don't. The
> problem was I couldn't tag as both natural=water to get the rendering
> and natural=bay to indicate the type of feature.

Yes agreed, tagging the bay area seems like the right sort of thing to
do. I've had the problem with mulitvalued tags before - the ';'
approach seems rather hacky to me so I can understand why went for
bay.

>
> I've since realised that tagging as natural=water, water=bay could be
> a solution to use, but as natural=bay already had widespread use with
> nodes, I wanted to keep consistency.
>
> As Markus_g mentioned you could try to edit Navits stylesheets so it
> renders natural=bay areas as water (some times as a multipolygon),
> although...

Yep - I will look in to that but from looking in to the code it looks
hard(ish) as I don't see a generic approach for dealing with ways that
are concatenated to form closed way.

>
> I'm not opposed to your suggestion of keeping a kind of coastline tag,
> I'm just not sure the best way to implement it, please discuss it if
> you like.
>
> * Perhaps the coastline tag should be reserved for the ocean facing
> coast. If we want to tag anything say inside a bay or harbour maybe we
> could use a shoreline tag.

Yes, this where the definitions aren't entirely clear to me. At some
points we can say it's clearly coastline, at some points it's clearly
riverbank, but the transition is not so clear.

I suspect that the ways that make up a bay should be tagged with
something, they mark a transition between water and not-water and the
bay is the area inside these. The relation does this nicely.

> * A problem with tagging the area of a bay is that while the shoreline
> is mostly well defined, the other edge is fuzzy. A possible solution
> is to use a multi polygon relation to tag just the non-shoreline
> segments of the bay outline as fuzzy=*. I suppose that using a
> multipolygon relation you can keep jest the shoreline segments
> together in another relation for say a larger harbour or river....

Yes, there is an examples of this across Port Hacking with a coastline
tag runnnig across open water. Conceptually wrong I think, but needed
in practice fro rendering to have any chance.

Not that it helps, but it occurs to me that the rendering model may be
inverted. If the default was everywhere is water and then we have
closed areas of land then things may go smoother - but tool late now
;-)

Because of the way coastline rendering works I can't see a way to make
things render correctly without having at least one hack (i.e the fake
coastline boundary).

The least hacky approach that I can see if for the water/non-water
transition to be tagged coastline or riverbank (and shoreline if we
can define it sensibly). At the point of transition there will need to
be some tagging-for-the-rendere, but that's unavoidable.

cheers


>



-- 
Franc



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