[Tilesathome] steam over landuse

[Martin Koppenhoefer]

2009/2/5 D Tucny <d at tucny.com>:
- Zitierten Text anzeigen -
> 2009/2/4 Knut Arne Bjørndal <bob+osm at cakebox.net>
>>
>> On Wed, Feb 04, 2009 at 12:37:50PM +0100, Chris-Hein Lunkhusen wrote:
>> > D Tucny schrieb:
>> >
>> > >  <http://www.informationfreeway.org/?lat=51.912&lon=7.737&zoom=16>
>> >
>> > > > But the stream is tagged as layer -1, so is underground as landuse
>> > > > will assume 0 (but render behind other layer 0 objects).
>> > >
>> > >     Yes, streams are often tagged as -1 so that they are rendered
>> > >     under streets. In Wiki there is also the recommendation to
>> > >     tag waterways as -1.
>> > >
>> > >     So landuse should never cover other objects.
>> > >     Landuse should be assumed as layer -100. ;-)
>>
>> Virtual landuse things like residential and industrial are done at -5
>> (the lowest layer osmarender processes).
>>
>> The practice of always tagging waterways as -1 sound stupid to me, the
>> layer tag is meant to describe where something is in relation to the
>> normal earth surface, and I'd say most streams are _at_ that height,
>> not (significantly) below it.
>>
>> > > I thought there was a discussion about this at some point in the past
>> > > and that the outcome was that the feeling was that landuse should be
>> > > drawn first, though allowing layers within the landuse 'layer' then
>> > > other features drawn over whatever the outcome of the landuse layer
>> > > was... which, would be effectively the same as making landuse
>> > > effectively exist at -100 to -90...
>> > > Can't remember the details, but will try and find the mails...
>> >
>> > It makes no sense that a "virtual" object like landuse
>> > covers any "real" object like streams or whatever, no matter
>> > what the layer is.
>>
>> As forests are physical objects they are drawn in the normal order.
>
> While forests are physical objects, they are drawn to represent an area, an
> area that could have objects running through it below the level of the
> surrounding land, tunnels, being a good example, but, I'd argue that water
> is lower too, unless you're at sea or are dealing with an aquaduct...
>
> I don't believe a forest should render over the top of a tunnel, I don't
> think it shouldn't obliterate any lower layer features, I believe it should
> just be drawn as a background layer...
>
> I have an example of a road tunnel running under a range of wooded hills,
> along the hills are footpaths, the tunnel passes under the woods and
> footpaths... The tunnel is tagged as tunnel=yes, layer=-1, the woods are
> tagged as natural=wood, no layer, the footpath is tagged as highway=footway,
> no layer... I don't think it would be the 'right thing' to tag the woods as
> layer -2 in this case just to make it render 'right' in the osmarender
> layer...
>
> So, I'd support forests and woods and marshes/wetlands/whatever the current
> accepted tag for them is that are also used to represent potentially large
> areas to also follow the same 'draw first' rule that landuse areas use...
>
> d
>

In the end you will have to tell for each and every feature, which is
his place in the rendering order, and it will never be OK for all
cases, because there are always exceptions in the real world that
noone had thought of before. I would really love to have dashed lines
for the contours of underlaying features *above* the overlapping area.
So you can see the limits of it even if it's border doesn't coincide
with the overlapping area's one, and even when it is completely
covered.

Tunnels should IMHO render above most map objects  the same as
mentioned before, that is a dashed line (for tunnels the lines are
already like this by now), regardless of their actual layer.

Martin