[talk-au] NSW Transport Data Exchange (TDX)

Michael Gratton mike at vee.net
Wed Jan 23 02:53:49 GMT 2013

On 23/01/13 09:48, Ian Sergeant wrote:
> But the TDX data is updated very regularly, so if I fix a bus stop
> today,  how do you know whether you should overwrite that with the
> next revision of TDX data tomorrow?

Not really. They may regenerate the feed frequently, but the data rarely
changes (unless you're talking about the real-time feed, but I'm not,
I'm talking about stop locations and perhaps routes). From experience,
stops rarely change, routes change perhaps yearly, and even temporary
alterations due to works occur on a scale of months.

> That certainly defines the nature of the challenge.  I'd be happy to
> see the spec of exactly how you think we can stir this into our data
> soup. If you intend retaining user created data while discarding the
> imported data, you're likely creating the exact issue that the data
> issuers wish to avoid.

The high-level is pretty simple, conceptually. Once initially imported,
you need a bot running somewhere that does the following:

1. Downloads the feed file, say once per day
2. Generates a list of changes from the last good version downloaded
3. For every change, merge it with OSM

As indicated above, a merge should happen infrequently. The merge
process can be something like:

1. Look for the features that correspond to those that are being changed
(custom props can help here, failing that look for similar features nearby)
2. If found and if unmodified by another user since the import or last
update (perhaps the common case?), apply the change
4. Otherwise flag it as needing attention

Similarly for additions, and deletions.

So the bot acts much like an individual contributor, except that it uses
the feed as a data source rather than GPS.


⊨ Michael Gratton, Percept Wrangler.
⚙ <http://mjog.vee.net/>

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