[Tilesathome] Mixed tiles rendered incorrectly and a couple of other questions

[D Tucny]

Hi...

On 15/11/2007, tah at mcmurph.de <tah at mcmurph.de> wrote:
>
> Hi everyone,
>
> I have observed that some mixed tiles (sea or rivers and land) screw up
> (not randomly, but consistently on every re-render).
> Take a look here:
>
> http://www.informationfreeway.org/?lat=9.982127571086878&lon=105.8568767334366&zoom=12&layers=0B00F000
> There's a river with a riverbank and some tiles are just fine but some
> obviously think they are sea tiles. How to fix that?
> Water's always on the "right" side. This also happens with coast areas
> without riverbanks/islands and also with islands in the sea.


I've just had a look at the area, most of the riverbank is tagged
natural=water, but the narrower branch has two ways on top of each other,
one is natural=water, the other is waterway=river... If they are riverbank,
they should be waterway=riverbank, but the handling of this is somewhat more
difficult than for example natural=water with both banks needing to be a
single split way, though how this is now handled post 0.5 I'm not sure...
By the way, waterway=river is for say marking the middle of a narrow river
such that it would be drawn as a blue line, not sure if it would work as an
area...
As far as the water goes, I can't see anything that would make that not
render correctly, but, removing one of the ways on that one section would
help work out if something was going wrong there... I'll try and get my
local renderer back up and running and have a better look in the next couple
of days...


Yesterday I noticed that there are new commands available on
> informationfreeway.org with which I assume you can mark tiles as sea, land
> or mixed. Is this mentioned/explained anywhere? I don't see any effect,
> though. Plus the marking score seems to increase by 0.1 from tile to tile.
> Does this make sense?


It was mentioned a few times in the mailing list, but I can't find it now...
Basically it sends off the info to a server which records the remarking,
then someone can download that info and make a new oceantiles file at some
point... This is used by the tiles at home renderers so that they know how to
return an empty tile, also it seems, so they can do some other magic in
certain cases... As far as I know, this doesn't do anything with mapnik's
rendering...

Another question: how to mark green riverbanks/islands? I used the
> following:
> landuse:forest
> layer:1
> name:somename
> Is this correct? But if there's no forest, just green, what value to use?


The islands seem to be rotating the wrong way, the ways are describing land,
so the object of should be enclose by the way shouldn't it? i.e. contents to
the right, so, clockwise... Also, they should be tagged to describe what is
there, rather than what colour you want them to appear on the map, so,
natural=lane would be a better choice than landuse=forest...

If the water was natural=coastline, then an island could also be tagged
natural=coastline with the way pointing anticlockwise, this is because it's
describing the water which is outside the island rather than the island
itself, if that makes sense...


How to name cities with international names in PotLatch? I read that one
> should use name.en or name:en but I think PotLatch is buggy there.


Not sure about bugs in Potlatch, but, as far as I know, that sort of tagging
does work in Potlatch... the method is name:<language code>=name so, name:en
for english, name:fr for french, name:de for german etc, along with  just
name=name for the 'default' name which would typically be the local language
name...

Mapnik seems to have some coastline data. Why is this not available in the
> OSM data? It's quite tedious to do the coastline and knowing it's already
> there (although maybe not as exact as you could do it by hand or satellite,
> but it would be a good start).


The mapnik coastline data is from the pgs coastline shape files, at least
once you zoom in past a certain point... mapnik works with a number of types
of data, the OSM data is converted to a format that mapnik can use for
rendering, but, mapnik can also render shapefiles, so they are dropped in
directly... There is import work being done to convert and import these
shape files into the OSM database, see
http://wiki.openstreetmap.org/index.php/Coastlines, this is a quite long
process, especially as the data isn't perfect, there are gaps where there
were clouds, there are some other random gaps and there are other issues
with the fact that it doesn't contain information about which side is water,
so the scripts make an attempt at guessing, as such, all data once converted
needs to be reviewed and tidied up which as you can guess takes a lot of
time... It does look like there is already some coastline data in your area,
have you done this manually?

I hope this helps...

d
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