Thanks for the reply.
On 29/12/2015 21:09, Paul Norman wrote:
On 12/29/2015 9:41 AM, Dave F. wrote:
I've previously download a file of all OSM data within a rectangular
area. I then use mkgmap to convert it to the format by my Garmin
GPSr. In the future I'd like to change that so it's a multi faceted
polygon of only specified OSM entities.
At present, each time I want to update the file, I'm downloading
every entity, even if they haven't been amended. What I need is to
download any changes within the polygon since I last updated. I read
about minute, hourly & daily diffs. Am I able to state the date I
last updated as the start point for new data?
There appear to be a few programs able to do what I require, but
unsure which is best suited. Is Osmosis a bit overblown for my
purpose. Osmupdate seems a bit more lightweight. Osmconvert appears
to discourage doing what I need:
http://wiki.openstreetmap.org/wiki/Osmupdate#Use_Cases. Overpass also
has a way to download diffs. Anyone used that?
Your best bet is to get an extract from Geofabrik which contains the
areas you need and use their daily diffs to keep it up to date. If you
need a smaller area, extract it from this larger file every day.
A couple of problems with that, I'm afraid. Firstly they don't provide
my area & secondly I'm trying to avoid large downloads like the 670mb
England file & amendment files for data I'm never going to need. Is
there not a way to work just within a user specified polygon?
Is it better to work with a raw OSM data file or use a .pbf file? In
fact I'm a bit confused what one is. From the wiki it firstly says
"alternative to the XML format", but then goes on to compare it with
a compressed file format. Which is it?
OSM PBFs are raw OSM data, as is OSM XML and o5m. They're just
different file formats. Avoid OSM XML unless you're using software
which only supports that. Use PBF or o5m instead. PBF is easier to use
with the workflow I describe above since you can download a PBF
directly from Geofabrik.
So it's the original OSM(XML) fie format that's been compressed into a
PBF container, similar in concept to zip files?
Cheers
Dave F.
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