[OSM-dev] Visualising change (.osc) files

[S Knox]

Hi List,


I am already on the talk list, but this is my first post here. Hope it makes some semblance of sense.

Having seen Osmdiff in action, I thought it would be useful to have a mechanism to see daily changes to the database over a wider area (e.g. a region or a country), and/or without quite so much downloading, processing and hard disk space usage* (not that it's not a great tool). This could use either the full daily changeset or the changeset filtered by a bounding box. Of course, there are currently no facilities to visualise this at the moment, as way nodes are not included in the diff file (understandably). So is there some way that modified ways could be cross-referenced with an existing Postgis database to then enable all changes to be uploaded to a separate Postgis database. I was thinking about the steps necessary to achieve this and came up with the following.

1) Any added nodes are added to the "Change" Postgis database - should be relatively easy as already have location in changeset
2) Any changed nodes are added to the "Change" Postgis database in a similar way
3) Any changed ways query the "Existing" Postgis database and get the list of nodes and their locations. The entire way is then added to the "Change" database.
4) Deleted nodes/ways - this could also query the database and get the old geographic information.
5) The output could then be visualised in Mapnik or similar.

Is there something I haven't thought through, and what are the likely coding implications? I can tinker around with Perl, Python and Java, but when it comes to a large program like Osmosis I am a little lost to be honest.

For info there was a thread some while back on how it was impossible to filter a changeset by bounding box, and what alterations might be necessary to Osmosis to allow this to happen:
http://www.nabble.com/Osmosis:-Bounding-polygon-does-not-support-change-data-as-input--td19546267.html

However, I think this is a distinct task.

Cheers

Steve

* Currently using Osmdiff to see a change in a small area involves downloading 2 planet files of interest, likely to be > 90MB compressed, and then run osmosis on both for the area in question, then run osmdiff. Maybe I'm being a download-a-phobe as I only have mobile broadband (thanks the crapness of BT and the inability of Ofcom to have a competitive fixed line market) but that seems like a lot of work to me.


      
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