>> 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.
That's why I like the new replicate diffs. Has anyone done - and kept - a complete database dump before migrating from 0.4 to 0.5 or is the history (at least partially) lost? >> 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. Thanks for the history tour. I didn't know all that. Sounds a bit like the "Wild West of OSM" :) But I can't quite follow the multipolygon problem. I thought that _every_ old segment has been migrated to 0.5 in one way [sic!] or another and I would "only" prepend the history I can find to these existing ways. Am I thinking too simple here? >> - 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. I can certainly appreciate that decision. I just want to understand what would be needed and decide if it is worthwhile to do something about it or not. Lars _______________________________________________ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/dev
