i'm starting to wonder if we're talking about 2 separate issues that
lead to similar outcomes.
coastlines break because:
1. they get broken in the extraction process because the poly is too tight
2. they get broken in the splitting process
a separate coastline file would quite likely mend both issues in the
same go by creating the coastline out of external data. only drawback:
if the poly for extracting the country is too tight, then there'd be an
empty area between the coast and the rest of the map data, so all the
beach bars are missing.
Am 29.08.2011 09:03, schrieb Bartosz Fabianowski:
geofabrik extracts are to blame - they're too "tight" in some places, so
the coastline breaks in the extraction process already
In a sense, this is true. However, *no* polygon can ever be guaranteed
to contain enough data. Even if Geofabrik used a bounding box instead
of a bounding polygon so that data for the entire region containing
the extract was available, coastlines would still break. It is the
rounding of tile boundaries in the splitter that pushes them beyond
the region of the original extract. The only robust solution is to
extract coastlines separately, for a larger region of the map.
I generated poly files for these countries which simply extend roughly
10 km into the neighbouring countries and the broken coastlines vanish,
even if the splitter splits the coastline in these places.
Do you use these poly files to extract coastlines only or do you use
them for all your data? In the former case, you are doing what I found
to be a good workaround. In the latter case, you are increasing the
region for which coastlines are available while also increasing the
region for which tiles are built. If the coastlines happen to work
with the new regions, that is great - but it is coincidental, not
guaranteed :(.
- Bartosz
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