[OSM-dev] Complete history of OSM data - questions and discussion

[Frederik Ramm]

Hi,

Lars Francke wrote:
> I had not thought of that. When I first used OSM, segments were long
> gone so I tend to forget those. There are a few planet dumps from
> those time but none before 060403 and no diffs (which would be
> required to fully reconstruct the history). 

No, diffs only show the changes between two points in time, not what 
happened in between; so they cannot be used to fully reconstruct history.

> While I'm of course
> interested in the most complete history possible I don't know if this
> data would be easy to integrate. 

No, it would probably be hard.

> As I understand it all the old
> segments that weren't part of a way were converted to a way and all
> 0.4-ways were just migrated to 0.5-ways (segments to node reference).
> I suppose segments that were part of at least one way were not
> converted to a way?

I think so too, but I am unsure what happened to tagged segments. Also 
we used to have lots of "unordered ways" where a number of segments were 
part of a way but not in a sorted order. Sometimes they weren't even 
contingent and thus had to be split in multiple ways when 0.5 was 
introduced. Also, we used this deliberately to model areas with holes 
(two chains of segments, one clockwise, one counter-clockwise, being 
part of the same way - that was your area with a hole!). These would 
have to be retro-fitted into multipolygons for every point in history. 
It is not difficult to do it once but to do it for two points in history 
and hope to assign the resulting changes to the same virtual relation id 
is... a challenge.

> - For ways we'd need to find the history data of the segments they
> were made of and "merge" that into the history of the way, again
> requiring versions before "1"

Yes, we briefly thought about something like that when we did the 
0.4-0.5 migration (a synthesized history if you will) but dropped the 
idea due to its complexity.

Bye
Frederik