----- Original Message -----
From: "Paul Norman" <[email protected]>
To: <[email protected]>
Sent: Monday, January 30, 2012 5:09 AM
Subject: [OSM-dev] Coastline shapefiles
I have been experimenting with generating the coastline shapefiles locally
using http://svn.openstreetmap.org/applications/utils/coastcheck/ and
ended
up with a few questions
1. Is this the same code that is currently used to generate the
processed_p
files?
2. It took my server about one hour from the start of extracting the
coastline data to creating the shapefiles. My understanding was that this
process took about a day. I'm using a different route to extract coastline
data than osm2coast, could this account for the difference?
3. If I were to run the coastline generation daily and upload the files
somewhere, could someone then host a slippymap showing coastline errors?
Firstly , is a slippy map showing coastline errors really necessary? If you
could upload the error point shapefile somewhere daily I'm sure you would
find these errors were corrected within a few hours. Michal Migurski has
been generating coastline error files every 3 - 4 weeks
http://metro.teczno.com/#coastline, and recently I've been finding that by
the time I try and correct the errors someone has got there first.
Secondly , if my memory serves me correctly, the original coastline error
map showed both points where there was a disconnect in the coastline, and
also places where there were geometry issues (mainly the small artefacts
left over form the PGS import). These errors were I believe displayed on
the slippy map by way of transparent tiles, and obviously there was time
taken to generate these tiles, and then bandwidth / space requirements
involved in deploying them.
Recently ( last 3 - 4 months) the number of disconnects has been reduced to
a low number, and it is now possible to deploy a slippy map much more
simply, see http://www.wightpaths.co.uk/coast/ and hosting requirements for
this are therefore minimal, if it was felt a coastline error map was useful.
The number of the second type of error (geometry issues) is still quite
high, and probably the only way to show these on a slippy map would be to go
down the transparent tile route, though I guess some form of clustering of
marker points would be possible. I do wonder though what the benefit of
showing these on a slippy map would be. Over the last few months I've been
going round clearing these errors up, and will continue to do so. I think I
have reduced the number by about 2 / 3 rds so quantity wise it is not an
impossible task.
If at the end there are any remaining errors they are likely to be two
causes:
a) these are in Canada - Paul you are probably aware of my posting to the
talk-ca list asking if it was worth my effort in clearing these up due to
the possibility of wholesale replacement of the current coastline data with
Canvec data
b) clearing up the error is too complex. I know this is may sound like an
excuse, but there was at least one area in the USA where a latter import of
data with ways tagged as natural = water over the top of PGS ways tagged as
natural = coastline, made a quick resolution of the problem difficult, and I
gave up and moved to another area. Without wishing to sound arrogant, if
someone needs a slippy map to identify the errors, then they are probably
not the right person to go about sorting out the issue in this particular
circumstance. ( BTW that's not a comment aimed at you Paul - if you're
running the coastline error files and can get GeoBase NHN into OSM then I
realise you are technically competent ; I'm just saying that crowdsourcing
coastline error issues may in fact lead to more errors being created than
are solved)
Anyway to summarise. My belief is that producing a slippy map showing the
coastline errors is not particularly necessary
Daily production, and upload to somewhere accessible, of the error points
shapefilefile ,and to a lesser extent the processed_p shapefile, would be
very useful
David
4. Given that it only took an hour to generate, is there any way to get
more
frequent updates to the coastline files?
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