[OSM-dev] Representing differences between sets of OSM data

[Jon Burgess]

On Sun, 2007-08-19 at 19:10 +0200, Martijn van Oosterhout wrote:
> Hi,
> 
> >From the looks of it there are at least three ways of representing
> changes to OSM data:
> 
> 1. The format used by JOSM (adds action=(modify|delete)) to entities
> 2. The format used by the planetdiff (used add/delete entities)
> 3. The osmChange format used by osmosis (can't find docs on this)
> 
> Now, I don't really want to have to support all of these at once, so
> does anyone have any recommendations about which one is the best to
> use, and if there are any conversion programs that can convert between
> them.

I think the different file formats reflect the different aims of the
applications. In addition to the obvious format differences between JOSM
and planetdiff, the applications store different data in the files. 

In JOSM you get data which is unmodified too. Also the data in JOSM is
complete, i.e. if there is a way, then you also have the relevant
segments and nodes which it references. In the planetdiff this is not
the case. The planetdiff may have information saying a <seg> was added
to a way but may not include any other information about the underlying
<segment>.

In theory I could probably adapt the planetdiff format to be closer to
that used by JOSM but I'd need to be convinced it was really worth the
effort. I'd be against adding information about the unmodified nodes and
segments to the diff since this would increase the file size and also
break the streaming algorithm which the diff tool currently uses.

	Jon