[osmosis-dev] Need help understanding osmosis OsmChange structure

[Frederik Ramm]

Hi,

Daniel Caris wrote:
> Im trying to understand the structure behind the change sets (OsmChange) 
> produced by osmosis (in particular the daily updates).  A little 
> confused in regards to the ordering of modify and create xml-nodes, what 
> the changeset id’s refer to, what version numbers refer to, and the 
> general order in which changes (modify, create or delete) are processed in.

If you don't know what a changeset or an object version is, then what 
are you trying to do with OsmChange files?

The ordering is not specified, but generally the order is first nodes, 
then ways, then relations, and among each group ascending by id then 
version; you will find as many modify/create/delete xml nodes as 
necessitated by this order.

Which order changes are processed in depends on whoever processes them 
and for what purpose. A typical Osmosis --apply-change task will consume 
one stream of entities and one stream of changes and expect them both to 
be sorted, applying changes one after the other.

Changesets are an OSM concept to group a number of changes and apply a 
comment and possibly futher information to them. There is no strict 
relation to OsmChange files; all changes contained in one Changeset 
could be expressed as one OsmChange file, but you could also have one 
OsmChange file that describes everything changed within a certain time 
and that might only contain part of a Changeset.

Bye
Frederik