[OSM-dev] Get geometries out of OSM changes file

[François Lacombe]

Le lun. 22 mars 2021 à 00:50, Roland Olbricht <roland.olbricht at gmx.de> a
écrit :

> Ahem, yes and no.
>

Understood, thank you to make this clear to me.

Thank you to Norbert for extra situations.
Note that a "delete" change doesn't have to be linked on its own to any
admin boundary nor be counted: it refers to the last existing version
(which had been created or edited and counted every day of its lifetime).


> Have I understood it correctly that the ultimate task is to compute per
> day and per each of the 40k municipalities the number of changes and of
> resulting matching objects, over a timespan of some years?
>

Yes, that's it. 40k municipalities plus regions as well (a given feature
can be linked to several boundaries).

This process should be done not only daily but may have to catch up on any
delay for any reason (mainly for database failure or new functionality
implementation after the start of a project).

As Pierre mentioned, it's possible to compare daily extracts of planet to
get geometries day by day but it's not possible when you have to catch up
on 6 months back.
It's what we do today: our database is updated with minute diffs and a
script runs each night to count every objects linked to appropriate
boundaries.
Even if we miss some intraday versions it's not an as big loss as it could
be over several months.

Current catch up at a national scale is easy by using osmium tags-filter as
it doesn't require any geometry to be operated.
https://github.com/vdct/ProjetDuMois/blob/master/db/10_project_update.js#L333

I understand now the only valid solution would be to use an OSHDB, right?
Can it be refreshed every day? I occasionally use OSHome dashboard and it
only gets 10 updates a year, doesn't it?

All the best

François
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